<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019e92e9-5361-79c4-a8e6-6c98b33ecece,g:d2b82721-4156-40df-9dd8-8cc05b35b735-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.xanadu.ai/role/ConsolidatedBalanceSheets" xlink:type="simple" xlink:href="xndu-20260630.xsd#ConsolidatedBalanceSheets"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/ConsolidatedBalanceSheets" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019e92e9-5414-756c-b36d-687582672ed7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019e92e9-5414-7d89-b4ba-7ccdc3b48b08" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019e92e9-5414-756c-b36d-687582672ed7" xlink:to="loc_us-gaap_StatementTable_019e92e9-5414-7d89-b4ba-7ccdc3b48b08" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019e92e9-5414-727f-b8d4-f559af07042c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019e92e9-5414-7d89-b4ba-7ccdc3b48b08" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019e92e9-5414-727f-b8d4-f559af07042c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019e92e9-5414-727f-b8d4-f559af07042c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019e92e9-5414-727f-b8d4-f559af07042c" xlink:to="loc_us-gaap_ClassOfStockDomain_019e92e9-5414-727f-b8d4-f559af07042c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019e92e9-5414-76d7-ad26-773528ab99b7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019e92e9-5414-727f-b8d4-f559af07042c" xlink:to="loc_us-gaap_ClassOfStockDomain_019e92e9-5414-76d7-ad26-773528ab99b7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_OldXanaduCommonStockMember_019e92e9-5414-748c-a002-dcba4b1eecfb" xlink:href="xndu-20260630.xsd#xndu_OldXanaduCommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019e92e9-5414-76d7-ad26-773528ab99b7" xlink:to="loc_xndu_OldXanaduCommonStockMember_019e92e9-5414-748c-a002-dcba4b1eecfb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_CommonClassAAndClassBMember_019e92e9-5414-712f-b02c-ff8e1695754c" xlink:href="xndu-20260630.xsd#xndu_CommonClassAAndClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019e92e9-5414-76d7-ad26-773528ab99b7" xlink:to="loc_xndu_CommonClassAAndClassBMember_019e92e9-5414-712f-b02c-ff8e1695754c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_019e92e9-5414-759d-b268-298be1004795" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e92e9-5414-756c-b36d-687582672ed7" xlink:to="loc_us-gaap_AssetsAbstract_019e92e9-5414-759d-b268-298be1004795" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrentAbstract_019e92e9-5414-7bef-b4bd-3cbda17c4800" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019e92e9-5414-759d-b268-298be1004795" xlink:to="loc_us-gaap_AssetsCurrentAbstract_019e92e9-5414-7bef-b4bd-3cbda17c4800" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019e92e9-5414-7ccd-a4d2-4122a4f95bda" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019e92e9-5414-7bef-b4bd-3cbda17c4800" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019e92e9-5414-7ccd-a4d2-4122a4f95bda" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivablesNetCurrent_019e92e9-5414-760c-bdb1-c8c3294470d6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReceivablesNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019e92e9-5414-7bef-b4bd-3cbda17c4800" xlink:to="loc_us-gaap_ReceivablesNetCurrent_019e92e9-5414-760c-bdb1-c8c3294470d6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MaterialsSuppliesAndOther_019e92e9-5414-7c54-a7ce-b0e866ed3716" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MaterialsSuppliesAndOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019e92e9-5414-7bef-b4bd-3cbda17c4800" xlink:to="loc_us-gaap_MaterialsSuppliesAndOther_019e92e9-5414-7c54-a7ce-b0e866ed3716" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_019e92e9-5414-76c9-83e8-b78f769a4476" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019e92e9-5414-7bef-b4bd-3cbda17c4800" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_019e92e9-5414-76c9-83e8-b78f769a4476" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_019e92e9-5414-7a59-8eb8-d08ae2e14dc2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019e92e9-5414-7bef-b4bd-3cbda17c4800" xlink:to="loc_us-gaap_AssetsCurrent_019e92e9-5414-7a59-8eb8-d08ae2e14dc2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019e92e9-5414-7d80-bf57-364b5b94096c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019e92e9-5414-759d-b268-298be1004795" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019e92e9-5414-7d80-bf57-364b5b94096c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_019e92e9-5414-709e-bf07-0a3544bea589" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019e92e9-5414-759d-b268-298be1004795" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_019e92e9-5414-709e-bf07-0a3544bea589" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019e92e9-5414-7071-9ce1-ebcba7675796" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019e92e9-5414-759d-b268-298be1004795" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019e92e9-5414-7071-9ce1-ebcba7675796" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepositsAssetsNoncurrent_019fa700-862f-7ccd-8ca6-55a79ca08dce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepositsAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019e92e9-5414-759d-b268-298be1004795" xlink:to="loc_us-gaap_DepositsAssetsNoncurrent_019fa700-862f-7ccd-8ca6-55a79ca08dce" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_019e92e9-5414-72fb-bb32-8369f80686ab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019e92e9-5414-759d-b268-298be1004795" xlink:to="loc_us-gaap_Assets_019e92e9-5414-72fb-bb32-8369f80686ab" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019e92e9-5414-7bd9-97a4-28997881ff28" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e92e9-5414-756c-b36d-687582672ed7" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019e92e9-5414-7bd9-97a4-28997881ff28" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_019e92e9-5414-7e69-801d-fec40401a5cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019e92e9-5414-7bd9-97a4-28997881ff28" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_019e92e9-5414-7e69-801d-fec40401a5cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_019e92e9-5414-7e63-a40e-ea4d7676bb4d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019e92e9-5414-7e69-801d-fec40401a5cc" xlink:to="loc_us-gaap_AccountsPayableCurrent_019e92e9-5414-7e63-a40e-ea4d7676bb4d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesCurrent_019e92e9-5414-7b49-8b35-deb40f81e70e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019e92e9-5414-7e69-801d-fec40401a5cc" xlink:to="loc_us-gaap_AccruedLiabilitiesCurrent_019e92e9-5414-7b49-8b35-deb40f81e70e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_019e92e9-5414-758e-8a78-3eb6a6b9baaf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019e92e9-5414-7e69-801d-fec40401a5cc" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_019e92e9-5414-758e-8a78-3eb6a6b9baaf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeCurrent_019e92e9-5414-7238-997c-e945acb64fe5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredIncomeCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019e92e9-5414-7e69-801d-fec40401a5cc" xlink:to="loc_us-gaap_DeferredIncomeCurrent_019e92e9-5414-7238-997c-e945acb64fe5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityCurrent_019e92e9-5414-7047-b881-8211129b9537" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019e92e9-5414-7e69-801d-fec40401a5cc" xlink:to="loc_us-gaap_OperatingLeaseLiabilityCurrent_019e92e9-5414-7047-b881-8211129b9537" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_019f88f3-f49b-7506-ae0a-66151c16db50" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019e92e9-5414-7e69-801d-fec40401a5cc" xlink:to="loc_us-gaap_LongTermDebtCurrent_019f88f3-f49b-7506-ae0a-66151c16db50" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantsAndRightsOutstanding_019e92e9-5414-7bed-8143-773211b81ab6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantsAndRightsOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019e92e9-5414-7e69-801d-fec40401a5cc" xlink:to="loc_us-gaap_WarrantsAndRightsOutstanding_019e92e9-5414-7bed-8143-773211b81ab6" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_019e92e9-5414-7241-be93-1c2890e88bb0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019e92e9-5414-7e69-801d-fec40401a5cc" xlink:to="loc_us-gaap_LiabilitiesCurrent_019e92e9-5414-7241-be93-1c2890e88bb0" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_019e92e9-5414-7860-945f-250ab65e20fa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019e92e9-5414-7bd9-97a4-28997881ff28" xlink:to="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_019e92e9-5414-7860-945f-250ab65e20fa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_019e92e9-5414-7b52-a954-7c4e03a2e215" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019e92e9-5414-7bd9-97a4-28997881ff28" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_019e92e9-5414-7b52-a954-7c4e03a2e215" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_019e92e9-5414-74f1-8299-ae69bc42b916" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019e92e9-5414-7bd9-97a4-28997881ff28" xlink:to="loc_us-gaap_Liabilities_019e92e9-5414-74f1-8299-ae69bc42b916" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingencies_019e92e9-5414-7f18-8a7f-4c32aadd1b77" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommitmentsAndContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019e92e9-5414-7bd9-97a4-28997881ff28" xlink:to="loc_us-gaap_CommitmentsAndContingencies_019e92e9-5414-7f18-8a7f-4c32aadd1b77" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityAbstract_019e92e9-5414-70ea-b7e9-660c36707fe1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019e92e9-5414-7bd9-97a4-28997881ff28" xlink:to="loc_us-gaap_StockholdersEquityAbstract_019e92e9-5414-70ea-b7e9-660c36707fe1" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_019e92e9-5414-7481-99a9-6d50ab07f24c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityCarryingAmountAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019e92e9-5414-70ea-b7e9-660c36707fe1" xlink:to="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_019e92e9-5414-7481-99a9-6d50ab07f24c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_019e92e9-5414-7627-8f46-614ebb3ca1cf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019e92e9-5414-70ea-b7e9-660c36707fe1" xlink:to="loc_us-gaap_CommonStockValue_019e92e9-5414-7627-8f46-614ebb3ca1cf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapital_019e92e9-5414-7acf-8e1b-e85ed42d2cf0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019e92e9-5414-70ea-b7e9-660c36707fe1" xlink:to="loc_us-gaap_AdditionalPaidInCapital_019e92e9-5414-7acf-8e1b-e85ed42d2cf0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019e92e9-5414-7188-96c4-9d06e75cc854" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019e92e9-5414-70ea-b7e9-660c36707fe1" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019e92e9-5414-7188-96c4-9d06e75cc854" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019e92e9-5414-7834-bd20-5257854d91d4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019e92e9-5414-70ea-b7e9-660c36707fe1" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019e92e9-5414-7834-bd20-5257854d91d4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019e92e9-5414-71c4-8a35-90f07d8f6936" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019e92e9-5414-70ea-b7e9-660c36707fe1" xlink:to="loc_us-gaap_StockholdersEquity_019e92e9-5414-71c4-8a35-90f07d8f6936" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_019e92e9-5414-7a1f-9415-91c7807b34e3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019e92e9-5414-7bd9-97a4-28997881ff28" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_019e92e9-5414-7a1f-9415-91c7807b34e3" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/ConsolidatedBalanceSheetsParenthetical" xlink:type="simple" xlink:href="xndu-20260630.xsd#ConsolidatedBalanceSheetsParenthetical"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/ConsolidatedBalanceSheetsParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019e92e9-5414-7ad6-98e1-84fe3ee31fbf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019e92e9-5414-7532-88b7-9633fa062de6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019e92e9-5414-7ad6-98e1-84fe3ee31fbf" xlink:to="loc_us-gaap_StatementTable_019e92e9-5414-7532-88b7-9633fa062de6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019e92e9-5414-74a7-be4b-b8d1df603dc9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019e92e9-5414-7532-88b7-9633fa062de6" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019e92e9-5414-74a7-be4b-b8d1df603dc9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019e92e9-5414-74a7-be4b-b8d1df603dc9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019e92e9-5414-74a7-be4b-b8d1df603dc9" xlink:to="loc_us-gaap_ClassOfStockDomain_019e92e9-5414-74a7-be4b-b8d1df603dc9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019e92e9-5414-7f74-a814-8a7230d760b2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019e92e9-5414-74a7-be4b-b8d1df603dc9" xlink:to="loc_us-gaap_ClassOfStockDomain_019e92e9-5414-7f74-a814-8a7230d760b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_OldXanaduCommonStockMember_019e92e9-5414-7199-bbb8-dec88338b580" xlink:href="xndu-20260630.xsd#xndu_OldXanaduCommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019e92e9-5414-7f74-a814-8a7230d760b2" xlink:to="loc_xndu_OldXanaduCommonStockMember_019e92e9-5414-7199-bbb8-dec88338b580" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019e92e9-5414-785e-8ab6-aabf9cfa0ad0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019e92e9-5414-7f74-a814-8a7230d760b2" xlink:to="loc_us-gaap_CommonClassAMember_019e92e9-5414-785e-8ab6-aabf9cfa0ad0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_019e92e9-5414-7b16-90b8-c981d43a368c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019e92e9-5414-7f74-a814-8a7230d760b2" xlink:to="loc_us-gaap_CommonClassBMember_019e92e9-5414-7b16-90b8-c981d43a368c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesAuthorized_019faace-14ee-769e-ab1d-ba591fa0950e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquitySharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e92e9-5414-7ad6-98e1-84fe3ee31fbf" xlink:to="loc_us-gaap_TemporaryEquitySharesAuthorized_019faace-14ee-769e-ab1d-ba591fa0950e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesIssued_019faace-14ee-7347-9b0b-5c1fae6a92fa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquitySharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e92e9-5414-7ad6-98e1-84fe3ee31fbf" xlink:to="loc_us-gaap_TemporaryEquitySharesIssued_019faace-14ee-7347-9b0b-5c1fae6a92fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesOutstanding_019faace-14ee-7a7a-a4e9-bd9112032a78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquitySharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e92e9-5414-7ad6-98e1-84fe3ee31fbf" xlink:to="loc_us-gaap_TemporaryEquitySharesOutstanding_019faace-14ee-7a7a-a4e9-bd9112032a78" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_019e92e9-5414-7600-b3cc-a6cd264643d3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e92e9-5414-7ad6-98e1-84fe3ee31fbf" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_019e92e9-5414-7600-b3cc-a6cd264643d3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_019e92e9-5414-7abd-a661-07d7068c66b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e92e9-5414-7ad6-98e1-84fe3ee31fbf" xlink:to="loc_us-gaap_CommonStockSharesIssued_019e92e9-5414-7abd-a661-07d7068c66b3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019e92e9-5414-73ea-b23a-de37598ca6aa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e92e9-5414-7ad6-98e1-84fe3ee31fbf" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019e92e9-5414-73ea-b23a-de37598ca6aa" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_019f66e8-35be-71ed-9e86-e5e0c5279601" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e92e9-5414-7ad6-98e1-84fe3ee31fbf" xlink:to="loc_us-gaap_LongTermDebtCurrent_019f66e8-35be-71ed-9e86-e5e0c5279601" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/ConsolidatedStatementsofShareholdersEquityUnaudited" xlink:type="simple" xlink:href="xndu-20260630.xsd#ConsolidatedStatementsofShareholdersEquityUnaudited"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/ConsolidatedStatementsofShareholdersEquityUnaudited" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019e92e9-5414-7b02-92c6-af167e6aa084" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019e92e9-5414-7e46-af25-2f6a1d41d4eb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019e92e9-5414-7b02-92c6-af167e6aa084" xlink:to="loc_us-gaap_StatementTable_019e92e9-5414-7e46-af25-2f6a1d41d4eb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019e92e9-5414-7dac-b633-7a63841c55b1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019e92e9-5414-7e46-af25-2f6a1d41d4eb" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019e92e9-5414-7dac-b633-7a63841c55b1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019e92e9-5414-7dac-b633-7a63841c55b1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019e92e9-5414-7dac-b633-7a63841c55b1" xlink:to="loc_us-gaap_ClassOfStockDomain_019e92e9-5414-7dac-b633-7a63841c55b1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019e92e9-5414-7988-8f51-8c0c51032e7c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019e92e9-5414-7dac-b633-7a63841c55b1" xlink:to="loc_us-gaap_ClassOfStockDomain_019e92e9-5414-7988-8f51-8c0c51032e7c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_OldXanaduConvertiblePreferredSharesMember_019e92e9-5414-731c-8003-275516f8d28e" xlink:href="xndu-20260630.xsd#xndu_OldXanaduConvertiblePreferredSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019e92e9-5414-7988-8f51-8c0c51032e7c" xlink:to="loc_xndu_OldXanaduConvertiblePreferredSharesMember_019e92e9-5414-731c-8003-275516f8d28e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_OldXanaduCommonStockMember_019e92e9-5414-72e8-9316-e23d63d8bdb2" xlink:href="xndu-20260630.xsd#xndu_OldXanaduCommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019e92e9-5414-7988-8f51-8c0c51032e7c" xlink:to="loc_xndu_OldXanaduCommonStockMember_019e92e9-5414-72e8-9316-e23d63d8bdb2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_CommonClassAAndClassBMember_019e92e9-5414-7bbb-93d6-dadfd9a139ff" xlink:href="xndu-20260630.xsd#xndu_CommonClassAAndClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019e92e9-5414-7988-8f51-8c0c51032e7c" xlink:to="loc_xndu_CommonClassAAndClassBMember_019e92e9-5414-7bbb-93d6-dadfd9a139ff" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019e92e9-5414-75c5-a0e8-42ec37f9fbe8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019e92e9-5414-7e46-af25-2f6a1d41d4eb" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019e92e9-5414-75c5-a0e8-42ec37f9fbe8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019e92e9-5414-75c5-a0e8-42ec37f9fbe8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019e92e9-5414-75c5-a0e8-42ec37f9fbe8" xlink:to="loc_us-gaap_EquityComponentDomain_019e92e9-5414-75c5-a0e8-42ec37f9fbe8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019e92e9-5414-7457-b840-c2c22765c347" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019e92e9-5414-75c5-a0e8-42ec37f9fbe8" xlink:to="loc_us-gaap_EquityComponentDomain_019e92e9-5414-7457-b840-c2c22765c347" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ShareCapitalMember_019e92e9-5414-7c75-8bf4-e25a581895ac" xlink:href="xndu-20260630.xsd#xndu_ShareCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019e92e9-5414-7457-b840-c2c22765c347" xlink:to="loc_xndu_ShareCapitalMember_019e92e9-5414-7c75-8bf4-e25a581895ac" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019e92e9-5414-7e9f-bade-2204866b6637" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ShareCapitalMember_019e92e9-5414-7c75-8bf4-e25a581895ac" xlink:to="loc_us-gaap_CommonStockMember_019e92e9-5414-7e9f-bade-2204866b6637" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019e92e9-5414-7364-ba3f-48a56e26420d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019e92e9-5414-7457-b840-c2c22765c347" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019e92e9-5414-7364-ba3f-48a56e26420d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019e92e9-5414-7f34-a141-1fc68e1190d7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019e92e9-5414-7457-b840-c2c22765c347" xlink:to="loc_us-gaap_RetainedEarningsMember_019e92e9-5414-7f34-a141-1fc68e1190d7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019e92e9-5414-7071-9faa-210f9a374388" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019e92e9-5414-7457-b840-c2c22765c347" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019e92e9-5414-7071-9faa-210f9a374388" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementAxis_019e92e9-5414-71ec-b572-e64dfdd14420" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019e92e9-5414-7e46-af25-2f6a1d41d4eb" xlink:to="loc_srt_RestatementAxis_019e92e9-5414-71ec-b572-e64dfdd14420" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_019e92e9-5414-71ec-b572-e64dfdd14420_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RestatementAxis_019e92e9-5414-71ec-b572-e64dfdd14420" xlink:to="loc_srt_RestatementDomain_019e92e9-5414-71ec-b572-e64dfdd14420_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_019e92e9-5414-76ef-9407-4ec1a9a1fc87" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RestatementAxis_019e92e9-5414-71ec-b572-e64dfdd14420" xlink:to="loc_srt_RestatementDomain_019e92e9-5414-76ef-9407-4ec1a9a1fc87" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioPreviouslyReportedMember_019e92e9-5414-7bad-9293-241c54d578ee" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioPreviouslyReportedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RestatementDomain_019e92e9-5414-76ef-9407-4ec1a9a1fc87" xlink:to="loc_srt_ScenarioPreviouslyReportedMember_019e92e9-5414-7bad-9293-241c54d578ee" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementAdjustmentMember_019e92e9-5414-768b-b038-ca4d534a2ac6" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RestatementDomain_019e92e9-5414-76ef-9407-4ec1a9a1fc87" xlink:to="loc_srt_RestatementAdjustmentMember_019e92e9-5414-768b-b038-ca4d534a2ac6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-5414-7b76-b10a-4b04c57cea75" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e92e9-5414-7b02-92c6-af167e6aa084" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-5414-7b76-b10a-4b04c57cea75" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019e92e9-5414-7553-9c9d-10391eb63c1e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-5414-7b76-b10a-4b04c57cea75" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019e92e9-5414-7553-9c9d-10391eb63c1e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019e92e9-5414-7ee3-94cb-a1a72438bcdb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-5414-7b76-b10a-4b04c57cea75" xlink:to="loc_us-gaap_StockholdersEquity_019e92e9-5414-7ee3-94cb-a1a72438bcdb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_019e92e9-5414-7597-8657-f6a7fe3f8c8c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-5414-7b76-b10a-4b04c57cea75" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_019e92e9-5414-7597-8657-f6a7fe3f8c8c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities_019e92e9-5414-7b70-b837-2f10a7ae6d5e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-5414-7b76-b10a-4b04c57cea75" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities_019e92e9-5414-7b70-b837-2f10a7ae6d5e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019e92e9-5414-7060-bf04-8165dbb31be1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-5414-7b76-b10a-4b04c57cea75" xlink:to="loc_us-gaap_NetIncomeLoss_019e92e9-5414-7060-bf04-8165dbb31be1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019e92e9-5414-7b47-825d-92f42c05f0ec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-5414-7b76-b10a-4b04c57cea75" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019e92e9-5414-7b47-825d-92f42c05f0ec" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019e92e9-5414-75bb-bd3b-6af09f987d44" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-5414-7b76-b10a-4b04c57cea75" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019e92e9-5414-75bb-bd3b-6af09f987d44" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_StockIssuedDuringPeriodValueStockOptionsExercisedNetOfAdjustments_019fc413-77a1-71f2-abe6-db544d832948" xlink:href="xndu-20260630.xsd#xndu_StockIssuedDuringPeriodValueStockOptionsExercisedNetOfAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-5414-7b76-b10a-4b04c57cea75" xlink:to="loc_xndu_StockIssuedDuringPeriodValueStockOptionsExercisedNetOfAdjustments_019fc413-77a1-71f2-abe6-db544d832948" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_019e92e9-5414-7ca0-9f4e-d872aaa74928" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-5414-7b76-b10a-4b04c57cea75" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_019e92e9-5414-7ca0-9f4e-d872aaa74928" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_StockIssuedDuringPeriodSharesReverseRecapitalization_019e92e9-5414-745c-8b70-af450f33f1fa" xlink:href="xndu-20260630.xsd#xndu_StockIssuedDuringPeriodSharesReverseRecapitalization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-5414-7b76-b10a-4b04c57cea75" xlink:to="loc_xndu_StockIssuedDuringPeriodSharesReverseRecapitalization_019e92e9-5414-745c-8b70-af450f33f1fa" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_StockIssuedDuringPeriodValueReverseRecapitalization_019e92e9-5414-7285-9f73-140d6ea25214" xlink:href="xndu-20260630.xsd#xndu_StockIssuedDuringPeriodValueReverseRecapitalization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-5414-7b76-b10a-4b04c57cea75" xlink:to="loc_xndu_StockIssuedDuringPeriodValueReverseRecapitalization_019e92e9-5414-7285-9f73-140d6ea25214" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_StockReclassifiedDuringPeriodDerivativeLiabilityContingentConsiderationValue_019e92e9-5414-7e10-9508-910822e77f6d" xlink:href="xndu-20260630.xsd#xndu_StockReclassifiedDuringPeriodDerivativeLiabilityContingentConsiderationValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-5414-7b76-b10a-4b04c57cea75" xlink:to="loc_xndu_StockReclassifiedDuringPeriodDerivativeLiabilityContingentConsiderationValue_019e92e9-5414-7e10-9508-910822e77f6d" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfUnits_019f8968-1b31-750b-9dbf-908f7c98ef9e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueConversionOfUnits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-5414-7b76-b10a-4b04c57cea75" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfUnits_019f8968-1b31-750b-9dbf-908f7c98ef9e" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019fa711-94b9-763c-85a9-1945f53519d0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-5414-7b76-b10a-4b04c57cea75" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019fa711-94b9-763c-85a9-1945f53519d0" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_019fa711-94b9-70d5-9249-6245bfde6c21" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-5414-7b76-b10a-4b04c57cea75" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_019fa711-94b9-70d5-9249-6245bfde6c21" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesIssuedForServices_019fa711-94b9-7e3c-8afd-bf35fb97b55b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesIssuedForServices"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-5414-7b76-b10a-4b04c57cea75" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesIssuedForServices_019fa711-94b9-7e3c-8afd-bf35fb97b55b" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueIssuedForServices_019fa711-94b9-7e9d-abed-659572a37529" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueIssuedForServices"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-5414-7b76-b10a-4b04c57cea75" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueIssuedForServices_019fa711-94b9-7e9d-abed-659572a37529" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued_019e92e9-5414-796a-a104-fd958ace99b1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-5414-7b76-b10a-4b04c57cea75" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued_019e92e9-5414-796a-a104-fd958ace99b1" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_StockIssuedDuringPeriodSharesExerciseOfWarrants_019e92e9-5414-7491-9a50-3213a873c045" xlink:href="xndu-20260630.xsd#xndu_StockIssuedDuringPeriodSharesExerciseOfWarrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-5414-7b76-b10a-4b04c57cea75" xlink:to="loc_xndu_StockIssuedDuringPeriodSharesExerciseOfWarrants_019e92e9-5414-7491-9a50-3213a873c045" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_StockIssuedDuringPeriodValueExerciseOfWarrants_019e92e9-5414-78be-89af-7d928b982918" xlink:href="xndu-20260630.xsd#xndu_StockIssuedDuringPeriodValueExerciseOfWarrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-5414-7b76-b10a-4b04c57cea75" xlink:to="loc_xndu_StockIssuedDuringPeriodValueExerciseOfWarrants_019e92e9-5414-78be-89af-7d928b982918" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_019e92e9-5414-7b14-8496-5d4a3746848d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-5414-7b76-b10a-4b04c57cea75" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_019e92e9-5414-7b14-8496-5d4a3746848d" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019e92e9-5414-71c6-acc2-028030224550" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019e92e9-5414-752b-9fb2-aa00300c4cf9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_019faaba-a1c6-7828-8f96-e2fb24fc425b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInTemporaryEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e92e9-5414-7b02-92c6-af167e6aa084" xlink:to="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_019faaba-a1c6-7828-8f96-e2fb24fc425b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesOutstanding_019faab9-f634-7f31-b7ef-0bd04f32ba60" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquitySharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_019faaba-a1c6-7828-8f96-e2fb24fc425b" xlink:to="loc_us-gaap_TemporaryEquitySharesOutstanding_019faab9-f634-7f31-b7ef-0bd04f32ba60" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_019faaba-1851-7191-b73d-0a2f25a688de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityCarryingAmountAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_019faaba-a1c6-7828-8f96-e2fb24fc425b" xlink:to="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_019faaba-1851-7191-b73d-0a2f25a688de" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_TemporaryEquitySharesConversionOfConvertibleSecurities_019faac5-2227-740e-8d53-e74b6cdbe75d" xlink:href="xndu-20260630.xsd#xndu_TemporaryEquitySharesConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_019faaba-a1c6-7828-8f96-e2fb24fc425b" xlink:to="loc_xndu_TemporaryEquitySharesConversionOfConvertibleSecurities_019faac5-2227-740e-8d53-e74b6cdbe75d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_TemporaryEquityValueConversionOfConvertibleSecurities_019faac5-3bc6-7658-a04d-71cab130f988" xlink:href="xndu-20260630.xsd#xndu_TemporaryEquityValueConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_019faaba-a1c6-7828-8f96-e2fb24fc425b" xlink:to="loc_xndu_TemporaryEquityValueConversionOfConvertibleSecurities_019faac5-3bc6-7658-a04d-71cab130f988" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesOutstanding_019faabb-17e6-7d1a-b64b-94656db4d55d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquitySharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_019faabb-66a9-79ac-9804-829dba8de6cd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityCarryingAmountAttributableToParent"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesNarrativeDetails" xlink:type="simple" xlink:href="xndu-20260630.xsd#BasisofPresentationandSummaryofSignificantAccountingPoliciesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-5414-746a-846e-beb5cc0f215b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_019e92e9-5414-7e44-b9de-8eef76e6a329" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-5414-746a-846e-beb5cc0f215b" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_019e92e9-5414-7e44-b9de-8eef76e6a329" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019fb198-ab32-7254-8499-758d66fa4584" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019e92e9-5414-7e44-b9de-8eef76e6a329" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019fb198-ab32-7254-8499-758d66fa4584" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019fb198-ab32-7254-8499-758d66fa4584_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019fb198-ab32-7254-8499-758d66fa4584" xlink:to="loc_us-gaap_ClassOfStockDomain_019fb198-ab32-7254-8499-758d66fa4584_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019fb198-ab32-710b-9e56-294b77988d42" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019fb198-ab32-7254-8499-758d66fa4584" xlink:to="loc_us-gaap_ClassOfStockDomain_019fb198-ab32-710b-9e56-294b77988d42" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_XanaduClassBSubordinateVotingSharesEarnOutSharesMember_019fb198-ab32-7749-a085-c90b1ca9da88" xlink:href="xndu-20260630.xsd#xndu_XanaduClassBSubordinateVotingSharesEarnOutSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019fb198-ab32-710b-9e56-294b77988d42" xlink:to="loc_xndu_XanaduClassBSubordinateVotingSharesEarnOutSharesMember_019fb198-ab32-7749-a085-c90b1ca9da88" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019fb33c-c278-7927-9398-6f83da07d9b3" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019e92e9-5414-7e44-b9de-8eef76e6a329" xlink:to="loc_srt_CounterpartyNameAxis_019fb33c-c278-7927-9398-6f83da07d9b3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019fb33c-c278-7927-9398-6f83da07d9b3_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019fb33c-c278-7927-9398-6f83da07d9b3" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019fb33c-c278-7927-9398-6f83da07d9b3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019fb33c-c278-7f7b-93de-f306fde7dc52" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019fb33c-c278-7927-9398-6f83da07d9b3" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019fb33c-c278-7f7b-93de-f306fde7dc52" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_YorkvilleInvestorMember_019fb33c-c278-722e-9979-4dcab696e504" xlink:href="xndu-20260630.xsd#xndu_YorkvilleInvestorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019fb33c-c278-7f7b-93de-f306fde7dc52" xlink:to="loc_xndu_YorkvilleInvestorMember_019fb33c-c278-722e-9979-4dcab696e504" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019e92e9-5414-71d7-9b02-1914cd7b76a0" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019e92e9-5414-7e44-b9de-8eef76e6a329" xlink:to="loc_srt_RangeAxis_019e92e9-5414-71d7-9b02-1914cd7b76a0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e92e9-5414-71d7-9b02-1914cd7b76a0_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019e92e9-5414-71d7-9b02-1914cd7b76a0" xlink:to="loc_srt_RangeMember_019e92e9-5414-71d7-9b02-1914cd7b76a0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e92e9-5414-7eef-ac5d-772c3e7896e6" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019e92e9-5414-71d7-9b02-1914cd7b76a0" xlink:to="loc_srt_RangeMember_019e92e9-5414-7eef-ac5d-772c3e7896e6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019e92e9-5414-762f-8479-c248ec688e5c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019e92e9-5414-7eef-ac5d-772c3e7896e6" xlink:to="loc_srt_MinimumMember_019e92e9-5414-762f-8479-c248ec688e5c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019fb7ba-800b-7bbe-ad57-742c6ac7f8af" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019e92e9-5414-7eef-ac5d-772c3e7896e6" xlink:to="loc_srt_MaximumMember_019fb7ba-800b-7bbe-ad57-742c6ac7f8af" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019e92e9-5414-7329-8fad-bae000764508" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-5414-746a-846e-beb5cc0f215b" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019e92e9-5414-7329-8fad-bae000764508" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019e92e9-5414-72ee-9a59-b74bea48c8c3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-5414-746a-846e-beb5cc0f215b" xlink:to="loc_us-gaap_NetIncomeLoss_019e92e9-5414-72ee-9a59-b74bea48c8c3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019e92e9-5414-7e81-bcbf-f22aeaa3d8b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-5414-746a-846e-beb5cc0f215b" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019e92e9-5414-7e81-bcbf-f22aeaa3d8b3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019e92e9-5414-7aa1-bd35-13559e97a492" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-5414-746a-846e-beb5cc0f215b" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019e92e9-5414-7aa1-bd35-13559e97a492" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_WorkingCapitalNet_019e92e9-5414-702e-833d-78b4046e5716" xlink:href="xndu-20260630.xsd#xndu_WorkingCapitalNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-5414-746a-846e-beb5cc0f215b" xlink:to="loc_xndu_WorkingCapitalNet_019e92e9-5414-702e-833d-78b4046e5716" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ProceedsFromReverseRecapitalization_019e92e9-5414-7d2c-bb41-7f6b35e31995" xlink:href="xndu-20260630.xsd#xndu_ProceedsFromReverseRecapitalization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-5414-746a-846e-beb5cc0f215b" xlink:to="loc_xndu_ProceedsFromReverseRecapitalization_019e92e9-5414-7d2c-bb41-7f6b35e31995" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfPrivatePlacement_019e92e9-5414-77d3-ae8e-2815f6967918" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOfPrivatePlacement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-5414-746a-846e-beb5cc0f215b" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfPrivatePlacement_019e92e9-5414-77d3-ae8e-2815f6967918" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_CashAcquiredThroughReverseRecapitalization_019e92e9-5414-7d76-a22d-0d1c1bedd3fc" xlink:href="xndu-20260630.xsd#xndu_CashAcquiredThroughReverseRecapitalization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-5414-746a-846e-beb5cc0f215b" xlink:to="loc_xndu_CashAcquiredThroughReverseRecapitalization_019e92e9-5414-7d76-a22d-0d1c1bedd3fc" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromNotesPayable_019fb198-ab32-783c-8085-a2c30c4b4cca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromNotesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-5414-746a-846e-beb5cc0f215b" xlink:to="loc_us-gaap_ProceedsFromNotesPayable_019fb198-ab32-783c-8085-a2c30c4b4cca" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_DerivativeInstrumentContingentConsiderationLiabilityShares_019fb198-ab32-7a37-a24e-6acd1402cdfb" xlink:href="xndu-20260630.xsd#xndu_DerivativeInstrumentContingentConsiderationLiabilityShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-5414-746a-846e-beb5cc0f215b" xlink:to="loc_xndu_DerivativeInstrumentContingentConsiderationLiabilityShares_019fb198-ab32-7a37-a24e-6acd1402cdfb" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_DerivativeLiabilityContingentConsiderationRemainingSharesAvailableForIssuance_019fb198-ab32-7ada-a684-6ec1a8f462d9" xlink:href="xndu-20260630.xsd#xndu_DerivativeLiabilityContingentConsiderationRemainingSharesAvailableForIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-5414-746a-846e-beb5cc0f215b" xlink:to="loc_xndu_DerivativeLiabilityContingentConsiderationRemainingSharesAvailableForIssuance_019fb198-ab32-7ada-a684-6ec1a8f462d9" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentOfLongLivedAssetsToBeDisposedOf_019e92e9-5414-70fb-9d77-7cdac9ddbf02" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ImpairmentOfLongLivedAssetsToBeDisposedOf"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-5414-746a-846e-beb5cc0f215b" xlink:to="loc_us-gaap_ImpairmentOfLongLivedAssetsToBeDisposedOf_019e92e9-5414-70fb-9d77-7cdac9ddbf02" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_RevenueFromContractWithCustomerContractDuration_019e92e9-5414-7adf-9d15-8c94905fb7dc" xlink:href="xndu-20260630.xsd#xndu_RevenueFromContractWithCustomerContractDuration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-5414-746a-846e-beb5cc0f215b" xlink:to="loc_xndu_RevenueFromContractWithCustomerContractDuration_019e92e9-5414-7adf-9d15-8c94905fb7dc" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesScheduleofPropertyandEquipmentUsefulLifeDetails" xlink:type="simple" xlink:href="xndu-20260630.xsd#BasisofPresentationandSummaryofSignificantAccountingPoliciesScheduleofPropertyandEquipmentUsefulLifeDetails"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesScheduleofPropertyandEquipmentUsefulLifeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e92e9-5414-7e13-b21d-9aaa9ec264e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019e92e9-5414-78b2-a144-0f61ecef1227" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e92e9-5414-7e13-b21d-9aaa9ec264e8" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019e92e9-5414-78b2-a144-0f61ecef1227" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e92e9-5414-7341-a05b-6c250c411673" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019e92e9-5414-78b2-a144-0f61ecef1227" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e92e9-5414-7341-a05b-6c250c411673" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e92e9-5414-7341-a05b-6c250c411673_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e92e9-5414-7341-a05b-6c250c411673" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e92e9-5414-7341-a05b-6c250c411673_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e92e9-5414-70ec-a73c-883d2fc6b5dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e92e9-5414-7341-a05b-6c250c411673" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e92e9-5414-70ec-a73c-883d2fc6b5dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ComputerSystemsAndServersMember_019e92e9-5414-7a40-a08d-266e658080de" xlink:href="xndu-20260630.xsd#xndu_ComputerSystemsAndServersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e92e9-5414-70ec-a73c-883d2fc6b5dc" xlink:to="loc_xndu_ComputerSystemsAndServersMember_019e92e9-5414-7a40-a08d-266e658080de" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TechnologyEquipmentMember_019e92e9-5414-7ee3-9f61-a9d590d22cc1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TechnologyEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e92e9-5414-70ec-a73c-883d2fc6b5dc" xlink:to="loc_us-gaap_TechnologyEquipmentMember_019e92e9-5414-7ee3-9f61-a9d590d22cc1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComputerEquipmentMember_019e92e9-5414-7ae7-9cb5-1cff3457ef0f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ComputerEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e92e9-5414-70ec-a73c-883d2fc6b5dc" xlink:to="loc_us-gaap_ComputerEquipmentMember_019e92e9-5414-7ae7-9cb5-1cff3457ef0f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_019e92e9-5414-7e9b-a12e-5b6e7845a34d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FurnitureAndFixturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e92e9-5414-70ec-a73c-883d2fc6b5dc" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_019e92e9-5414-7e9b-a12e-5b6e7845a34d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_019e92e9-5414-7d2a-a8b7-74d2da0bde40" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e92e9-5414-7e13-b21d-9aaa9ec264e8" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_019e92e9-5414-7d2a-a8b7-74d2da0bde40" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesScheduleofFiniteLivedIntangibleAssetsUsefulLifeDetails" xlink:type="simple" xlink:href="xndu-20260630.xsd#BasisofPresentationandSummaryofSignificantAccountingPoliciesScheduleofFiniteLivedIntangibleAssetsUsefulLifeDetails"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesScheduleofFiniteLivedIntangibleAssetsUsefulLifeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e92e9-5414-7d34-bdfb-1f7df796baa7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019e92e9-5414-7952-90c0-2d1e4fbf2cea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e92e9-5414-7d34-bdfb-1f7df796baa7" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019e92e9-5414-7952-90c0-2d1e4fbf2cea" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019e92e9-5414-71de-b3ef-e7dbcb4d2a25" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019e92e9-5414-7952-90c0-2d1e4fbf2cea" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019e92e9-5414-71de-b3ef-e7dbcb4d2a25" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e92e9-5414-71de-b3ef-e7dbcb4d2a25_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019e92e9-5414-71de-b3ef-e7dbcb4d2a25" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e92e9-5414-71de-b3ef-e7dbcb4d2a25_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e92e9-5414-794f-bb07-0b496bdfd149" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019e92e9-5414-71de-b3ef-e7dbcb4d2a25" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e92e9-5414-794f-bb07-0b496bdfd149" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PatentsMember_019e92e9-5414-7047-8366-e1769a8c0d1e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PatentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e92e9-5414-794f-bb07-0b496bdfd149" xlink:to="loc_us-gaap_PatentsMember_019e92e9-5414-7047-8366-e1769a8c0d1e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareDevelopmentMember_019e92e9-5414-75be-b0fb-8516ff286690" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SoftwareDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e92e9-5414-794f-bb07-0b496bdfd149" xlink:to="loc_us-gaap_SoftwareDevelopmentMember_019e92e9-5414-75be-b0fb-8516ff286690" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwarePurchasedMember_019f3880-92d9-7933-9fb0-83dbd234132d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SoftwarePurchasedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e92e9-5414-794f-bb07-0b496bdfd149" xlink:to="loc_us-gaap_SoftwarePurchasedMember_019f3880-92d9-7933-9fb0-83dbd234132d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_019e92e9-5414-711c-8b49-27490ef3c6ac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e92e9-5414-7d34-bdfb-1f7df796baa7" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_019e92e9-5414-711c-8b49-27490ef3c6ac" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/ReverseRecapitalizationNarrativeDetails" xlink:type="simple" xlink:href="xndu-20260630.xsd#ReverseRecapitalizationNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/ReverseRecapitalizationNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ScheduleOfReverseRecapitalizationLineItems_019f6540-0952-7ec4-bfed-989a22bde99c" xlink:href="xndu-20260630.xsd#xndu_ScheduleOfReverseRecapitalizationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ScheduleOfReverseRecapitalizationTable_019e92e9-5414-77c8-9fd2-491bc7abfa5a" xlink:href="xndu-20260630.xsd#xndu_ScheduleOfReverseRecapitalizationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationLineItems_019f6540-0952-7ec4-bfed-989a22bde99c" xlink:to="loc_xndu_ScheduleOfReverseRecapitalizationTable_019e92e9-5414-77c8-9fd2-491bc7abfa5a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ReverseRecapitalizationWarrantExchangeComponentAxis_019f6540-2952-7534-a88e-a058b4bdae16" xlink:href="xndu-20260630.xsd#xndu_ReverseRecapitalizationWarrantExchangeComponentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationTable_019e92e9-5414-77c8-9fd2-491bc7abfa5a" xlink:to="loc_xndu_ReverseRecapitalizationWarrantExchangeComponentAxis_019f6540-2952-7534-a88e-a058b4bdae16" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ReverseRecapitalizationWarrantExchangeComponentDomain_019f6540-2952-7534-a88e-a058b4bdae16_default" xlink:href="xndu-20260630.xsd#xndu_ReverseRecapitalizationWarrantExchangeComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_xndu_ReverseRecapitalizationWarrantExchangeComponentAxis_019f6540-2952-7534-a88e-a058b4bdae16" xlink:to="loc_xndu_ReverseRecapitalizationWarrantExchangeComponentDomain_019f6540-2952-7534-a88e-a058b4bdae16_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ReverseRecapitalizationWarrantExchangeComponentDomain_019f6540-2952-79e0-9074-b080fe0a8849" xlink:href="xndu-20260630.xsd#xndu_ReverseRecapitalizationWarrantExchangeComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_xndu_ReverseRecapitalizationWarrantExchangeComponentAxis_019f6540-2952-7534-a88e-a058b4bdae16" xlink:to="loc_xndu_ReverseRecapitalizationWarrantExchangeComponentDomain_019f6540-2952-79e0-9074-b080fe0a8849" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_WarrantExchangeComponentOneMember_019f6540-2952-7e1d-84fb-e557f9a80060" xlink:href="xndu-20260630.xsd#xndu_WarrantExchangeComponentOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ReverseRecapitalizationWarrantExchangeComponentDomain_019f6540-2952-79e0-9074-b080fe0a8849" xlink:to="loc_xndu_WarrantExchangeComponentOneMember_019f6540-2952-7e1d-84fb-e557f9a80060" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_WarrantExchangeComponentTwoMember_019f6540-2952-7bb4-9428-bc665d0e5ba8" xlink:href="xndu-20260630.xsd#xndu_WarrantExchangeComponentTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ReverseRecapitalizationWarrantExchangeComponentDomain_019f6540-2952-79e0-9074-b080fe0a8849" xlink:to="loc_xndu_WarrantExchangeComponentTwoMember_019f6540-2952-7bb4-9428-bc665d0e5ba8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019f6540-2952-797c-ba93-d32c809c74f7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationTable_019e92e9-5414-77c8-9fd2-491bc7abfa5a" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019f6540-2952-797c-ba93-d32c809c74f7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019f6540-2952-797c-ba93-d32c809c74f7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019f6540-2952-797c-ba93-d32c809c74f7" xlink:to="loc_us-gaap_ClassOfStockDomain_019f6540-2952-797c-ba93-d32c809c74f7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019f6540-2952-71a3-888e-40aab2550508" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019f6540-2952-797c-ba93-d32c809c74f7" xlink:to="loc_us-gaap_ClassOfStockDomain_019f6540-2952-71a3-888e-40aab2550508" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_XanaduClassAMultipleVotingSharesMember_019f6540-2952-7067-9f54-33ebd344f25d" xlink:href="xndu-20260630.xsd#xndu_XanaduClassAMultipleVotingSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019f6540-2952-71a3-888e-40aab2550508" xlink:to="loc_xndu_XanaduClassAMultipleVotingSharesMember_019f6540-2952-7067-9f54-33ebd344f25d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_XanaduClassBSubordinateVotingSharesEarnOutSharesMember_019f6540-2952-7a3d-a928-af5498f1a689" xlink:href="xndu-20260630.xsd#xndu_XanaduClassBSubordinateVotingSharesEarnOutSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019f6540-2952-71a3-888e-40aab2550508" xlink:to="loc_xndu_XanaduClassBSubordinateVotingSharesEarnOutSharesMember_019f6540-2952-7a3d-a928-af5498f1a689" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ReverseRecapitalizationTermsOfEarnoutLiabilityAxis_019f6540-8d18-7207-aa3d-52044bfbc88e" xlink:href="xndu-20260630.xsd#xndu_ReverseRecapitalizationTermsOfEarnoutLiabilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationTable_019e92e9-5414-77c8-9fd2-491bc7abfa5a" xlink:to="loc_xndu_ReverseRecapitalizationTermsOfEarnoutLiabilityAxis_019f6540-8d18-7207-aa3d-52044bfbc88e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ReverseRecapitalizationTermsOfEarnoutLiabilityDomain_019f6540-8d18-7207-aa3d-52044bfbc88e_default" xlink:href="xndu-20260630.xsd#xndu_ReverseRecapitalizationTermsOfEarnoutLiabilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_xndu_ReverseRecapitalizationTermsOfEarnoutLiabilityAxis_019f6540-8d18-7207-aa3d-52044bfbc88e" xlink:to="loc_xndu_ReverseRecapitalizationTermsOfEarnoutLiabilityDomain_019f6540-8d18-7207-aa3d-52044bfbc88e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ReverseRecapitalizationTermsOfEarnoutLiabilityDomain_019f6540-8d18-726a-b115-bfd2f9812b8d" xlink:href="xndu-20260630.xsd#xndu_ReverseRecapitalizationTermsOfEarnoutLiabilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_xndu_ReverseRecapitalizationTermsOfEarnoutLiabilityAxis_019f6540-8d18-7207-aa3d-52044bfbc88e" xlink:to="loc_xndu_ReverseRecapitalizationTermsOfEarnoutLiabilityDomain_019f6540-8d18-726a-b115-bfd2f9812b8d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ReverseRecapitalizationEarnoutLiabilityTermsOneMember_019f6540-8d18-7ed2-b8b8-a751d0f582e0" xlink:href="xndu-20260630.xsd#xndu_ReverseRecapitalizationEarnoutLiabilityTermsOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ReverseRecapitalizationTermsOfEarnoutLiabilityDomain_019f6540-8d18-726a-b115-bfd2f9812b8d" xlink:to="loc_xndu_ReverseRecapitalizationEarnoutLiabilityTermsOneMember_019f6540-8d18-7ed2-b8b8-a751d0f582e0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ReverseRecapitalizationEarnoutLiabilityTermsTwoMember_019f6540-8d18-7017-97a8-5f012d9149c1" xlink:href="xndu-20260630.xsd#xndu_ReverseRecapitalizationEarnoutLiabilityTermsTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ReverseRecapitalizationTermsOfEarnoutLiabilityDomain_019f6540-8d18-726a-b115-bfd2f9812b8d" xlink:to="loc_xndu_ReverseRecapitalizationEarnoutLiabilityTermsTwoMember_019f6540-8d18-7017-97a8-5f012d9149c1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_019fc865-47de-750e-a495-4d03f2547b68" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationTable_019e92e9-5414-77c8-9fd2-491bc7abfa5a" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_019fc865-47de-750e-a495-4d03f2547b68" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019fc865-47de-750e-a495-4d03f2547b68_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019fc865-47de-750e-a495-4d03f2547b68" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019fc865-47de-750e-a495-4d03f2547b68_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019fc865-47de-7719-9b32-d04428f73529" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019fc865-47de-750e-a495-4d03f2547b68" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019fc865-47de-7719-9b32-d04428f73529" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_PIPEInvestorsMember_019fc865-5e65-79b2-9caf-a39d83769ba2" xlink:href="xndu-20260630.xsd#xndu_PIPEInvestorsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019fc865-47de-7719-9b32-d04428f73529" xlink:to="loc_xndu_PIPEInvestorsMember_019fc865-5e65-79b2-9caf-a39d83769ba2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ReverseRecapitalizationNumberOfShareClasses_019f6540-0952-77c7-8be7-48833b274fd2" xlink:href="xndu-20260630.xsd#xndu_ReverseRecapitalizationNumberOfShareClasses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationLineItems_019f6540-0952-7ec4-bfed-989a22bde99c" xlink:to="loc_xndu_ReverseRecapitalizationNumberOfShareClasses_019f6540-0952-77c7-8be7-48833b274fd2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockConvertibleConversionRatio_019f6540-0952-7d6e-9afa-fb4ec16d8a9e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockConvertibleConversionRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationLineItems_019f6540-0952-7ec4-bfed-989a22bde99c" xlink:to="loc_us-gaap_PreferredStockConvertibleConversionRatio_019f6540-0952-7d6e-9afa-fb4ec16d8a9e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_RecapitalizationExchangeRatio_019f6540-2952-7ffb-9255-c7ae665960d8" xlink:href="xndu-20260630.xsd#xndu_RecapitalizationExchangeRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationLineItems_019f6540-0952-7ec4-bfed-989a22bde99c" xlink:to="loc_xndu_RecapitalizationExchangeRatio_019f6540-2952-7ffb-9255-c7ae665960d8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019f6540-2952-7fa3-bfe6-d73c39bfbfad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationLineItems_019f6540-0952-7ec4-bfed-989a22bde99c" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019f6540-2952-7fa3-bfe6-d73c39bfbfad" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019f6540-2952-74da-9d53-2e90e536ecd9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationLineItems_019f6540-0952-7ec4-bfed-989a22bde99c" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019f6540-2952-74da-9d53-2e90e536ecd9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightOutstanding_019f6540-2952-79bb-97ae-00b40901ff5d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationLineItems_019f6540-0952-7ec4-bfed-989a22bde99c" xlink:to="loc_us-gaap_ClassOfWarrantOrRightOutstanding_019f6540-2952-79bb-97ae-00b40901ff5d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_019f6540-3f7c-7970-9149-df4722a185cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationLineItems_019f6540-0952-7ec4-bfed-989a22bde99c" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_019f6540-3f7c-7970-9149-df4722a185cb" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockPricePerShare_019f6540-3f7c-7bcd-a04d-7a8966b656c3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationLineItems_019f6540-0952-7ec4-bfed-989a22bde99c" xlink:to="loc_us-gaap_SaleOfStockPricePerShare_019f6540-3f7c-7bcd-a04d-7a8966b656c3" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_019f6540-3f7c-7b64-b794-32253cf868d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationLineItems_019f6540-0952-7ec4-bfed-989a22bde99c" xlink:to="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_019f6540-3f7c-7b64-b794-32253cf868d8" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_DerivativeInstrumentContingentConsiderationLiabilityShares_019f6540-3f7c-778e-ac63-e737752f0130" xlink:href="xndu-20260630.xsd#xndu_DerivativeInstrumentContingentConsiderationLiabilityShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationLineItems_019f6540-0952-7ec4-bfed-989a22bde99c" xlink:to="loc_xndu_DerivativeInstrumentContingentConsiderationLiabilityShares_019f6540-3f7c-778e-ac63-e737752f0130" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ProceedsFromReverseRecapitalization_019f6543-7dda-7d19-8255-86f157a57420" xlink:href="xndu-20260630.xsd#xndu_ProceedsFromReverseRecapitalization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationLineItems_019f6540-0952-7ec4-bfed-989a22bde99c" xlink:to="loc_xndu_ProceedsFromReverseRecapitalization_019f6543-7dda-7d19-8255-86f157a57420" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfPrivatePlacement_019f6543-7dda-75b8-9bc1-05115b143216" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOfPrivatePlacement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationLineItems_019f6540-0952-7ec4-bfed-989a22bde99c" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfPrivatePlacement_019f6543-7dda-75b8-9bc1-05115b143216" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_CashAcquiredThroughReverseRecapitalization_019f6540-67d8-7aec-8c2a-41db9814695c" xlink:href="xndu-20260630.xsd#xndu_CashAcquiredThroughReverseRecapitalization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationLineItems_019f6540-0952-7ec4-bfed-989a22bde99c" xlink:to="loc_xndu_CashAcquiredThroughReverseRecapitalization_019f6540-67d8-7aec-8c2a-41db9814695c" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ReverseRecapitalizationAcquisitionRelatedCostExpense_019f6540-67d8-7d1e-8ca0-3c760fafb6f6" xlink:href="xndu-20260630.xsd#xndu_ReverseRecapitalizationAcquisitionRelatedCostExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationLineItems_019f6540-0952-7ec4-bfed-989a22bde99c" xlink:to="loc_xndu_ReverseRecapitalizationAcquisitionRelatedCostExpense_019f6540-67d8-7d1e-8ca0-3c760fafb6f6" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ReverseRecapitalizationAcquisitionRelatedCostEquityInterestSharesIssuedExpense_019f6540-67d8-7009-bce9-35aa4deaa036" xlink:href="xndu-20260630.xsd#xndu_ReverseRecapitalizationAcquisitionRelatedCostEquityInterestSharesIssuedExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationLineItems_019f6540-0952-7ec4-bfed-989a22bde99c" xlink:to="loc_xndu_ReverseRecapitalizationAcquisitionRelatedCostEquityInterestSharesIssuedExpense_019f6540-67d8-7009-bce9-35aa4deaa036" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ReverseRecapitalizationAcquisitionRelatedCostLiabilityEarnoutPeriodExpense_019f6540-67d8-7e89-9fb3-32a4d256fec4" xlink:href="xndu-20260630.xsd#xndu_ReverseRecapitalizationAcquisitionRelatedCostLiabilityEarnoutPeriodExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationLineItems_019f6540-0952-7ec4-bfed-989a22bde99c" xlink:to="loc_xndu_ReverseRecapitalizationAcquisitionRelatedCostLiabilityEarnoutPeriodExpense_019f6540-67d8-7e89-9fb3-32a4d256fec4" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ReverseRecapitalizationAcquisitionRelatedCostEquityInterestShareCapitalExpense_019f6540-67d8-7f91-b160-d0fa2934eab2" xlink:href="xndu-20260630.xsd#xndu_ReverseRecapitalizationAcquisitionRelatedCostEquityInterestShareCapitalExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationLineItems_019f6540-0952-7ec4-bfed-989a22bde99c" xlink:to="loc_xndu_ReverseRecapitalizationAcquisitionRelatedCostEquityInterestShareCapitalExpense_019f6540-67d8-7f91-b160-d0fa2934eab2" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ReverseRecapitalizationAcquisitionRelatedCostIndirectCost_019f6540-67d8-7518-a274-fe96ebebb2b9" xlink:href="xndu-20260630.xsd#xndu_ReverseRecapitalizationAcquisitionRelatedCostIndirectCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationLineItems_019f6540-0952-7ec4-bfed-989a22bde99c" xlink:to="loc_xndu_ReverseRecapitalizationAcquisitionRelatedCostIndirectCost_019f6540-67d8-7518-a274-fe96ebebb2b9" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ReverseRecapitalizationAcquisitionRelatedCostIndirectCostExpenseIncurred_019f6540-67d8-7803-9300-94be36f75174" xlink:href="xndu-20260630.xsd#xndu_ReverseRecapitalizationAcquisitionRelatedCostIndirectCostExpenseIncurred"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationLineItems_019f6540-0952-7ec4-bfed-989a22bde99c" xlink:to="loc_xndu_ReverseRecapitalizationAcquisitionRelatedCostIndirectCostExpenseIncurred_019f6540-67d8-7803-9300-94be36f75174" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_DerivativeInstrumentContingentConsiderationLiabilityVestedShares_019f6540-8d18-757d-9504-333220353118" xlink:href="xndu-20260630.xsd#xndu_DerivativeInstrumentContingentConsiderationLiabilityVestedShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationLineItems_019f6540-0952-7ec4-bfed-989a22bde99c" xlink:to="loc_xndu_DerivativeInstrumentContingentConsiderationLiabilityVestedShares_019f6540-8d18-757d-9504-333220353118" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_DerivativeInstrumentContingentConsiderationLiabilityEarnoutPeriodStockPriceTrigger_019f6540-8d18-73fe-8760-87a18af59838" xlink:href="xndu-20260630.xsd#xndu_DerivativeInstrumentContingentConsiderationLiabilityEarnoutPeriodStockPriceTrigger"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationLineItems_019f6540-0952-7ec4-bfed-989a22bde99c" xlink:to="loc_xndu_DerivativeInstrumentContingentConsiderationLiabilityEarnoutPeriodStockPriceTrigger_019f6540-8d18-73fe-8760-87a18af59838" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_DerivativeInstrumentContingentConsiderationLiabilityEarnoutPeriodThresholdTradingDays_019f6540-8d18-74a9-91b3-08c4cf115665" xlink:href="xndu-20260630.xsd#xndu_DerivativeInstrumentContingentConsiderationLiabilityEarnoutPeriodThresholdTradingDays"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationLineItems_019f6540-0952-7ec4-bfed-989a22bde99c" xlink:to="loc_xndu_DerivativeInstrumentContingentConsiderationLiabilityEarnoutPeriodThresholdTradingDays_019f6540-8d18-74a9-91b3-08c4cf115665" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_DerivativeInstrumentContingentConsiderationLiabilityEarnoutPeriodThresholdConsecutiveTradingDays_019f6540-8d18-7bf3-b291-88a70016d123" xlink:href="xndu-20260630.xsd#xndu_DerivativeInstrumentContingentConsiderationLiabilityEarnoutPeriodThresholdConsecutiveTradingDays"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationLineItems_019f6540-0952-7ec4-bfed-989a22bde99c" xlink:to="loc_xndu_DerivativeInstrumentContingentConsiderationLiabilityEarnoutPeriodThresholdConsecutiveTradingDays_019f6540-8d18-7bf3-b291-88a70016d123" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilitiesCurrent_019f6540-aab4-7f6b-897b-473d7113acc7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationLineItems_019f6540-0952-7ec4-bfed-989a22bde99c" xlink:to="loc_us-gaap_DerivativeLiabilitiesCurrent_019f6540-aab4-7f6b-897b-473d7113acc7" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeGainLossOnDerivativeNet_019fc878-910e-7623-b5db-f57df929ed4c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeGainLossOnDerivativeNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationLineItems_019f6540-0952-7ec4-bfed-989a22bde99c" xlink:to="loc_us-gaap_DerivativeGainLossOnDerivativeNet_019fc878-910e-7623-b5db-f57df929ed4c" xlink:type="arc" order="24"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/ReverseRecapitalizationScheduleofSharesandVotingInterestOutstandingAfterReverseRecapitalizationandPIPEInvestmentDetails" xlink:type="simple" xlink:href="xndu-20260630.xsd#ReverseRecapitalizationScheduleofSharesandVotingInterestOutstandingAfterReverseRecapitalizationandPIPEInvestmentDetails"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/ReverseRecapitalizationScheduleofSharesandVotingInterestOutstandingAfterReverseRecapitalizationandPIPEInvestmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ReverseRecapitalizationLineItems_019e92e9-54be-7968-b808-cbb3e63fa059" xlink:href="xndu-20260630.xsd#xndu_ReverseRecapitalizationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ScheduleOfReverseRecapitalizationTable_019e92e9-5414-7912-975a-f8e726b86f60" xlink:href="xndu-20260630.xsd#xndu_ScheduleOfReverseRecapitalizationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_xndu_ReverseRecapitalizationLineItems_019e92e9-54be-7968-b808-cbb3e63fa059" xlink:to="loc_xndu_ScheduleOfReverseRecapitalizationTable_019e92e9-5414-7912-975a-f8e726b86f60" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019e92e9-5414-7c7f-8f12-0ac89d072588" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationTable_019e92e9-5414-7912-975a-f8e726b86f60" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019e92e9-5414-7c7f-8f12-0ac89d072588" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019e92e9-5414-7c7f-8f12-0ac89d072588_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019e92e9-5414-7c7f-8f12-0ac89d072588" xlink:to="loc_us-gaap_ClassOfStockDomain_019e92e9-5414-7c7f-8f12-0ac89d072588_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019e92e9-5414-79ea-b36a-b723ada59072" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019e92e9-5414-7c7f-8f12-0ac89d072588" xlink:to="loc_us-gaap_ClassOfStockDomain_019e92e9-5414-79ea-b36a-b723ada59072" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_XanaduClassAMultipleVotingSharesMember_019e92e9-5414-7e1f-ba77-6b22f465297c" xlink:href="xndu-20260630.xsd#xndu_XanaduClassAMultipleVotingSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019e92e9-5414-79ea-b36a-b723ada59072" xlink:to="loc_xndu_XanaduClassAMultipleVotingSharesMember_019e92e9-5414-7e1f-ba77-6b22f465297c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_XanaduClassBSubordinateVotingSharesEarnOutSharesMember_019e92e9-5414-79f5-84de-7cc346f8a478" xlink:href="xndu-20260630.xsd#xndu_XanaduClassBSubordinateVotingSharesEarnOutSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019e92e9-5414-79ea-b36a-b723ada59072" xlink:to="loc_xndu_XanaduClassBSubordinateVotingSharesEarnOutSharesMember_019e92e9-5414-79f5-84de-7cc346f8a478" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e92e9-5414-79da-b589-c89cebbf9959" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationTable_019e92e9-5414-7912-975a-f8e726b86f60" xlink:to="loc_dei_LegalEntityAxis_019e92e9-5414-79da-b589-c89cebbf9959" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e92e9-5414-79da-b589-c89cebbf9959_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e92e9-5414-79da-b589-c89cebbf9959" xlink:to="loc_dei_EntityDomain_019e92e9-5414-79da-b589-c89cebbf9959_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e92e9-5414-7f51-b98f-4d307a230b0f" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e92e9-5414-79da-b589-c89cebbf9959" xlink:to="loc_dei_EntityDomain_019e92e9-5414-7f51-b98f-4d307a230b0f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_OldXanaduShareholdersMember_019e92e9-54be-7459-965a-e64e43df42fb" xlink:href="xndu-20260630.xsd#xndu_OldXanaduShareholdersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e92e9-5414-7f51-b98f-4d307a230b0f" xlink:to="loc_xndu_OldXanaduShareholdersMember_019e92e9-54be-7459-965a-e64e43df42fb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_OldXanaduOptionsMember_019e92e9-54be-7826-a99c-aa47d6911eb8" xlink:href="xndu-20260630.xsd#xndu_OldXanaduOptionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e92e9-5414-7f51-b98f-4d307a230b0f" xlink:to="loc_xndu_OldXanaduOptionsMember_019e92e9-54be-7826-a99c-aa47d6911eb8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_OldXanaduWarrantsMember_019e92e9-54be-7a21-80d7-c26d7bad3d6e" xlink:href="xndu-20260630.xsd#xndu_OldXanaduWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e92e9-5414-7f51-b98f-4d307a230b0f" xlink:to="loc_xndu_OldXanaduWarrantsMember_019e92e9-54be-7a21-80d7-c26d7bad3d6e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_PIPEInvestorsMember_019e92e9-54be-7814-b4ad-522cfd1b3bf0" xlink:href="xndu-20260630.xsd#xndu_PIPEInvestorsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e92e9-5414-7f51-b98f-4d307a230b0f" xlink:to="loc_xndu_PIPEInvestorsMember_019e92e9-54be-7814-b4ad-522cfd1b3bf0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_SPACPublicShareholdersMember_019e92e9-54be-7aa6-89ab-0e020357429b" xlink:href="xndu-20260630.xsd#xndu_SPACPublicShareholdersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e92e9-5414-7f51-b98f-4d307a230b0f" xlink:to="loc_xndu_SPACPublicShareholdersMember_019e92e9-54be-7aa6-89ab-0e020357429b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_SPACPrivatePlacementShareholdersMember_019e92e9-54be-76af-a182-df6b94679fea" xlink:href="xndu-20260630.xsd#xndu_SPACPrivatePlacementShareholdersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e92e9-5414-7f51-b98f-4d307a230b0f" xlink:to="loc_xndu_SPACPrivatePlacementShareholdersMember_019e92e9-54be-76af-a182-df6b94679fea" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_SPACSponsorSharesMember_019e92e9-54be-7294-b1b0-14c0db37db07" xlink:href="xndu-20260630.xsd#xndu_SPACSponsorSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e92e9-5414-7f51-b98f-4d307a230b0f" xlink:to="loc_xndu_SPACSponsorSharesMember_019e92e9-54be-7294-b1b0-14c0db37db07" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019e92e9-54be-746e-bc13-7fbb8ec77924" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_xndu_ScheduleOfReverseRecapitalizationTable_019e92e9-5414-7912-975a-f8e726b86f60" xlink:to="loc_srt_CounterpartyNameAxis_019e92e9-54be-746e-bc13-7fbb8ec77924" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e92e9-54be-746e-bc13-7fbb8ec77924_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019e92e9-54be-746e-bc13-7fbb8ec77924" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e92e9-54be-746e-bc13-7fbb8ec77924_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e92e9-54be-7a86-b34a-4175a9c54394" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019e92e9-54be-746e-bc13-7fbb8ec77924" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e92e9-54be-7a86-b34a-4175a9c54394" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_SPACSponsorSharesMember_019e92e9-54be-798d-b820-86fcdbfbcf5a" xlink:href="xndu-20260630.xsd#xndu_SPACSponsorSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e92e9-54be-7a86-b34a-4175a9c54394" xlink:to="loc_xndu_SPACSponsorSharesMember_019e92e9-54be-798d-b820-86fcdbfbcf5a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019e92e9-54be-7f69-831c-baf71fa243bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ReverseRecapitalizationLineItems_019e92e9-54be-7968-b808-cbb3e63fa059" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019e92e9-54be-7f69-831c-baf71fa243bf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ReverseRecapitalizationVotingEquityInterestAcquiredPercentage_019e92e9-54be-7033-a517-c9926eaa3852" xlink:href="xndu-20260630.xsd#xndu_ReverseRecapitalizationVotingEquityInterestAcquiredPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ReverseRecapitalizationLineItems_019e92e9-54be-7968-b808-cbb3e63fa059" xlink:to="loc_xndu_ReverseRecapitalizationVotingEquityInterestAcquiredPercentage_019e92e9-54be-7033-a517-c9926eaa3852" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_CommonStockSharesOutstandingDiluted_019e92e9-54be-7924-a7a1-edeb8cbdb686" xlink:href="xndu-20260630.xsd#xndu_CommonStockSharesOutstandingDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ReverseRecapitalizationLineItems_019e92e9-54be-7968-b808-cbb3e63fa059" xlink:to="loc_xndu_CommonStockSharesOutstandingDiluted_019e92e9-54be-7924-a7a1-edeb8cbdb686" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ReverseRecapitalizationVotingEquityInterestAcquiredDilutedPercentage_019e92e9-54be-70f9-9e17-638d4e101404" xlink:href="xndu-20260630.xsd#xndu_ReverseRecapitalizationVotingEquityInterestAcquiredDilutedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ReverseRecapitalizationLineItems_019e92e9-54be-7968-b808-cbb3e63fa059" xlink:to="loc_xndu_ReverseRecapitalizationVotingEquityInterestAcquiredDilutedPercentage_019e92e9-54be-70f9-9e17-638d4e101404" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_DerivativeInstrumentContingentConsiderationLiabilityShares_019e92e9-54be-7b1c-b0ba-b234cea3a382" xlink:href="xndu-20260630.xsd#xndu_DerivativeInstrumentContingentConsiderationLiabilityShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ReverseRecapitalizationLineItems_019e92e9-54be-7968-b808-cbb3e63fa059" xlink:to="loc_xndu_DerivativeInstrumentContingentConsiderationLiabilityShares_019e92e9-54be-7b1c-b0ba-b234cea3a382" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/PropertyandEquipmentNetScheduleofPropertyandEquipmentDetails" xlink:type="simple" xlink:href="xndu-20260630.xsd#PropertyandEquipmentNetScheduleofPropertyandEquipmentDetails"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/PropertyandEquipmentNetScheduleofPropertyandEquipmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e92e9-54be-7211-960f-2c32d45e0e3a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019e92e9-54be-73e1-b46b-66a4dd992c85" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e92e9-54be-7211-960f-2c32d45e0e3a" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019e92e9-54be-73e1-b46b-66a4dd992c85" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e92e9-54be-7ae4-8506-66088cfc2970" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019e92e9-54be-73e1-b46b-66a4dd992c85" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e92e9-54be-7ae4-8506-66088cfc2970" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e92e9-54be-7ae4-8506-66088cfc2970_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e92e9-54be-7ae4-8506-66088cfc2970" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e92e9-54be-7ae4-8506-66088cfc2970_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e92e9-54be-7c50-aa4a-9ee974e60978" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e92e9-54be-7ae4-8506-66088cfc2970" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e92e9-54be-7c50-aa4a-9ee974e60978" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ComputerSystemsAndServersMember_019e92e9-54be-7414-9dc4-92d683edd0f2" xlink:href="xndu-20260630.xsd#xndu_ComputerSystemsAndServersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e92e9-54be-7c50-aa4a-9ee974e60978" xlink:to="loc_xndu_ComputerSystemsAndServersMember_019e92e9-54be-7414-9dc4-92d683edd0f2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComputerEquipmentMember_019e92e9-54be-7b40-a982-91c901f31355" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ComputerEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e92e9-54be-7c50-aa4a-9ee974e60978" xlink:to="loc_us-gaap_ComputerEquipmentMember_019e92e9-54be-7b40-a982-91c901f31355" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TechnologyEquipmentMember_019e92e9-54be-7800-9a9e-afe267b3dd0f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TechnologyEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e92e9-54be-7c50-aa4a-9ee974e60978" xlink:to="loc_us-gaap_TechnologyEquipmentMember_019e92e9-54be-7800-9a9e-afe267b3dd0f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_019e92e9-54be-74ef-86ef-022d56c1182a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FurnitureAndFixturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e92e9-54be-7c50-aa4a-9ee974e60978" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_019e92e9-54be-74ef-86ef-022d56c1182a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_019e92e9-54be-738a-8696-c8a03f79cef1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e92e9-54be-7c50-aa4a-9ee974e60978" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_019e92e9-54be-738a-8696-c8a03f79cef1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_019e92e9-54be-7b1f-aa58-639db7a5b6eb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e92e9-54be-7211-960f-2c32d45e0e3a" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_019e92e9-54be-7b1f-aa58-639db7a5b6eb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019e92e9-54be-775c-a470-1c2823e44253" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e92e9-54be-7211-960f-2c32d45e0e3a" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019e92e9-54be-775c-a470-1c2823e44253" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019e92e9-54be-78a8-844f-928714bc2f88" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e92e9-54be-7211-960f-2c32d45e0e3a" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019e92e9-54be-78a8-844f-928714bc2f88" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/IntangibleAssetsNetScheduleofFiniteLivedIntangibleAssetsDetails" xlink:type="simple" xlink:href="xndu-20260630.xsd#IntangibleAssetsNetScheduleofFiniteLivedIntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/IntangibleAssetsNetScheduleofFiniteLivedIntangibleAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e92e9-54be-71af-8193-b7a860b81c59" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019e92e9-54be-7ed7-b3e2-1f741e727c6f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e92e9-54be-71af-8193-b7a860b81c59" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019e92e9-54be-7ed7-b3e2-1f741e727c6f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019e92e9-54be-785f-ae88-499852c90282" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019e92e9-54be-7ed7-b3e2-1f741e727c6f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019e92e9-54be-785f-ae88-499852c90282" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e92e9-54be-785f-ae88-499852c90282_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019e92e9-54be-785f-ae88-499852c90282" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e92e9-54be-785f-ae88-499852c90282_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e92e9-54be-7ebb-a504-bbd7d1e63f00" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019e92e9-54be-785f-ae88-499852c90282" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e92e9-54be-7ebb-a504-bbd7d1e63f00" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PatentsMember_019e92e9-54be-7643-aca6-78773a0c0ff0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PatentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e92e9-54be-7ebb-a504-bbd7d1e63f00" xlink:to="loc_us-gaap_PatentsMember_019e92e9-54be-7643-aca6-78773a0c0ff0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareDevelopmentMember_019e92e9-54be-7662-aa46-e9e591745f0c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SoftwareDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e92e9-54be-7ebb-a504-bbd7d1e63f00" xlink:to="loc_us-gaap_SoftwareDevelopmentMember_019e92e9-54be-7662-aa46-e9e591745f0c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwarePurchasedMember_019f3880-e41d-78f2-a93e-00dd19120700" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SoftwarePurchasedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e92e9-54be-7ebb-a504-bbd7d1e63f00" xlink:to="loc_us-gaap_SoftwarePurchasedMember_019f3880-e41d-78f2-a93e-00dd19120700" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_019e92e9-54be-7240-9c10-41b1ceb78fa1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e92e9-54be-71af-8193-b7a860b81c59" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_019e92e9-54be-7240-9c10-41b1ceb78fa1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019e92e9-54be-7ab1-8693-6aa1ca01698d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e92e9-54be-71af-8193-b7a860b81c59" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019e92e9-54be-7ab1-8693-6aa1ca01698d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019e92e9-54be-7c72-8168-c3602753d790" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e92e9-54be-71af-8193-b7a860b81c59" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019e92e9-54be-7c72-8168-c3602753d790" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/DebtScheduleofLongTermDebtDetails" xlink:type="simple" xlink:href="xndu-20260630.xsd#DebtScheduleofLongTermDebtDetails"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/DebtScheduleofLongTermDebtDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019e92e9-54be-7336-8347-cdf1dd7f870d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019e92e9-54be-739a-b314-51be80710fa2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e92e9-54be-7336-8347-cdf1dd7f870d" xlink:to="loc_us-gaap_DebtInstrumentTable_019e92e9-54be-739a-b314-51be80710fa2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019e92e9-54be-7430-9ba2-b70e82e13547" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e92e9-54be-739a-b314-51be80710fa2" xlink:to="loc_us-gaap_DebtInstrumentAxis_019e92e9-54be-7430-9ba2-b70e82e13547" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019e92e9-54be-7430-9ba2-b70e82e13547_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019e92e9-54be-7430-9ba2-b70e82e13547" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019e92e9-54be-7430-9ba2-b70e82e13547_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019e92e9-54be-7e40-9a48-736eedea2286" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019e92e9-54be-7430-9ba2-b70e82e13547" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019e92e9-54be-7e40-9a48-736eedea2286" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_SIFLoanMember_019e92e9-54be-760d-9e0f-0ac8b31bdc15" xlink:href="xndu-20260630.xsd#xndu_SIFLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e92e9-54be-7e40-9a48-736eedea2286" xlink:to="loc_xndu_SIFLoanMember_019e92e9-54be-760d-9e0f-0ac8b31bdc15" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_FedDevLoanMember_019e92e9-54be-7e04-a01c-4a54b36f877c" xlink:href="xndu-20260630.xsd#xndu_FedDevLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e92e9-54be-7e40-9a48-736eedea2286" xlink:to="loc_xndu_FedDevLoanMember_019e92e9-54be-7e04-a01c-4a54b36f877c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019e92e9-54be-7bcc-8dc2-6951881fd0e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e92e9-54be-7336-8347-cdf1dd7f870d" xlink:to="loc_us-gaap_LongTermDebt_019e92e9-54be-7bcc-8dc2-6951881fd0e0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_019f25f8-dd64-7eb2-85bf-9dc1b85f4aa8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e92e9-54be-7336-8347-cdf1dd7f870d" xlink:to="loc_us-gaap_LongTermDebtCurrent_019f25f8-dd64-7eb2-85bf-9dc1b85f4aa8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_019f64fd-4887-7ec6-8173-3150354c1b62" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e92e9-54be-7336-8347-cdf1dd7f870d" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_019f64fd-4887-7ec6-8173-3150354c1b62" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/DebtNarrativeDetails" xlink:type="simple" xlink:href="xndu-20260630.xsd#DebtNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/DebtNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019e92e9-54be-72f3-8c8e-3ed1a4463d99" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019e92e9-54be-797a-94b2-c7fb446b1289" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e92e9-54be-72f3-8c8e-3ed1a4463d99" xlink:to="loc_us-gaap_DebtInstrumentTable_019e92e9-54be-797a-94b2-c7fb446b1289" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019e92e9-54be-7e6c-a731-559c68b69455" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e92e9-54be-797a-94b2-c7fb446b1289" xlink:to="loc_us-gaap_DebtInstrumentAxis_019e92e9-54be-7e6c-a731-559c68b69455" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019e92e9-54be-7e6c-a731-559c68b69455_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019e92e9-54be-7e6c-a731-559c68b69455" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019e92e9-54be-7e6c-a731-559c68b69455_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019e92e9-54be-7af0-9e4c-da15f5768cdd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019e92e9-54be-7e6c-a731-559c68b69455" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019e92e9-54be-7af0-9e4c-da15f5768cdd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_SIFLoanMember_019e92e9-54be-7389-bb7c-f4785b3a4e88" xlink:href="xndu-20260630.xsd#xndu_SIFLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e92e9-54be-7af0-9e4c-da15f5768cdd" xlink:to="loc_xndu_SIFLoanMember_019e92e9-54be-7389-bb7c-f4785b3a4e88" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_FedDevLoanMember_019e92e9-54be-7815-98af-67f188de656f" xlink:href="xndu-20260630.xsd#xndu_FedDevLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e92e9-54be-7af0-9e4c-da15f5768cdd" xlink:to="loc_xndu_FedDevLoanMember_019e92e9-54be-7815-98af-67f188de656f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_019e92e9-54be-7a37-a562-65e554bb9216" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e92e9-54be-72f3-8c8e-3ed1a4463d99" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_019e92e9-54be-7a37-a562-65e554bb9216" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_019e92e9-54be-762a-8130-b0e36d518f0d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOfLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e92e9-54be-72f3-8c8e-3ed1a4463d99" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_019e92e9-54be-762a-8130-b0e36d518f0d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_LongTermDebtPrincipalAndInterestRepaymentsPercentageOfPrincipalAmount_019e92e9-54be-7941-8865-8f21f5c9bcb5" xlink:href="xndu-20260630.xsd#xndu_LongTermDebtPrincipalAndInterestRepaymentsPercentageOfPrincipalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e92e9-54be-72f3-8c8e-3ed1a4463d99" xlink:to="loc_xndu_LongTermDebtPrincipalAndInterestRepaymentsPercentageOfPrincipalAmount_019e92e9-54be-7941-8865-8f21f5c9bcb5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_LongTermDebtRepaymentNumberOfAnnualInstallments_019e92e9-54be-7492-a460-0278ddbccac3" xlink:href="xndu-20260630.xsd#xndu_LongTermDebtRepaymentNumberOfAnnualInstallments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e92e9-54be-72f3-8c8e-3ed1a4463d99" xlink:to="loc_xndu_LongTermDebtRepaymentNumberOfAnnualInstallments_019e92e9-54be-7492-a460-0278ddbccac3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtWeightedAverageInterestRate_019e92e9-54be-7457-98cb-26867fdab4ec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtWeightedAverageInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e92e9-54be-72f3-8c8e-3ed1a4463d99" xlink:to="loc_us-gaap_LongtermDebtWeightedAverageInterestRate_019e92e9-54be-7457-98cb-26867fdab4ec" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_LongTermDebtRepaymentNumberOfMonthlyInstallments_019e92e9-54be-7789-b06e-92f93cdd54f5" xlink:href="xndu-20260630.xsd#xndu_LongTermDebtRepaymentNumberOfMonthlyInstallments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e92e9-54be-72f3-8c8e-3ed1a4463d99" xlink:to="loc_xndu_LongTermDebtRepaymentNumberOfMonthlyInstallments_019e92e9-54be-7789-b06e-92f93cdd54f5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_019f8978-6266-72cf-a954-5562b030af1d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e92e9-54be-72f3-8c8e-3ed1a4463d99" xlink:to="loc_us-gaap_LongTermDebtCurrent_019f8978-6266-72cf-a954-5562b030af1d" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/DebtScheduleofInterestExpenseDetails" xlink:type="simple" xlink:href="xndu-20260630.xsd#DebtScheduleofInterestExpenseDetails"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/DebtScheduleofInterestExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019f25fe-bfdd-7f4a-929a-47c68ce546cd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019f25fe-bfdd-7ecb-81d0-c04cf5d78313" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019f25fe-bfdd-7f4a-929a-47c68ce546cd" xlink:to="loc_us-gaap_DebtInstrumentTable_019f25fe-bfdd-7ecb-81d0-c04cf5d78313" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019f25fe-bfdd-74aa-9df1-d7dec794a40c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019f25fe-bfdd-7ecb-81d0-c04cf5d78313" xlink:to="loc_us-gaap_DebtInstrumentAxis_019f25fe-bfdd-74aa-9df1-d7dec794a40c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019f25fe-bfdd-74aa-9df1-d7dec794a40c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019f25fe-bfdd-74aa-9df1-d7dec794a40c" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019f25fe-bfdd-74aa-9df1-d7dec794a40c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019f25fe-bfdd-7fe2-ad32-fead679e819b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019f25fe-bfdd-74aa-9df1-d7dec794a40c" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019f25fe-bfdd-7fe2-ad32-fead679e819b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_SIFLoanMember_019f25fe-bfdd-767a-b1e4-c1d30f80b920" xlink:href="xndu-20260630.xsd#xndu_SIFLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019f25fe-bfdd-7fe2-ad32-fead679e819b" xlink:to="loc_xndu_SIFLoanMember_019f25fe-bfdd-767a-b1e4-c1d30f80b920" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseDebt_019f2608-d501-7bad-a65b-8b1ca6501c41" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestExpenseDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019f25fe-bfdd-7f4a-929a-47c68ce546cd" xlink:to="loc_us-gaap_InterestExpenseDebt_019f2608-d501-7bad-a65b-8b1ca6501c41" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/DebtScheduleofChangesinCarryingValueofLoansDetails" xlink:type="simple" xlink:href="xndu-20260630.xsd#DebtScheduleofChangesinCarryingValueofLoansDetails"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/DebtScheduleofChangesinCarryingValueofLoansDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019e92e9-54be-7eb8-840a-bd7cfd8b6389" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019e92e9-54be-7a82-8301-c874a717f19a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e92e9-54be-7eb8-840a-bd7cfd8b6389" xlink:to="loc_us-gaap_DebtInstrumentTable_019e92e9-54be-7a82-8301-c874a717f19a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019e92e9-54be-7cd4-992e-6bfc764bcc41" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e92e9-54be-7a82-8301-c874a717f19a" xlink:to="loc_us-gaap_DebtInstrumentAxis_019e92e9-54be-7cd4-992e-6bfc764bcc41" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019e92e9-54be-7cd4-992e-6bfc764bcc41_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019e92e9-54be-7cd4-992e-6bfc764bcc41" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019e92e9-54be-7cd4-992e-6bfc764bcc41_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019e92e9-54be-789a-bb67-a45c76ffea5d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019e92e9-54be-7cd4-992e-6bfc764bcc41" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019e92e9-54be-789a-bb67-a45c76ffea5d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_SIFLoanMember_019e92e9-54be-7c18-98f6-73d3fdd57ecf" xlink:href="xndu-20260630.xsd#xndu_SIFLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e92e9-54be-789a-bb67-a45c76ffea5d" xlink:to="loc_xndu_SIFLoanMember_019e92e9-54be-7c18-98f6-73d3fdd57ecf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_FedDevLoanMember_019e92e9-54be-71ab-b861-841f4a1ee3d3" xlink:href="xndu-20260630.xsd#xndu_FedDevLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e92e9-54be-789a-bb67-a45c76ffea5d" xlink:to="loc_xndu_FedDevLoanMember_019e92e9-54be-71ab-b861-841f4a1ee3d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ReconciliationOfCarryingValueOfLoansRollForward_019e92e9-54be-7af1-b4ff-682d95d3f419" xlink:href="xndu-20260630.xsd#xndu_ReconciliationOfCarryingValueOfLoansRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e92e9-54be-7eb8-840a-bd7cfd8b6389" xlink:to="loc_xndu_ReconciliationOfCarryingValueOfLoansRollForward_019e92e9-54be-7af1-b4ff-682d95d3f419" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019e92e9-54be-7861-9476-24164b7a1f10" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ReconciliationOfCarryingValueOfLoansRollForward_019e92e9-54be-7af1-b4ff-682d95d3f419" xlink:to="loc_us-gaap_LongTermDebt_019e92e9-54be-7861-9476-24164b7a1f10" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_LongTermDebtIncreaseDecreaseInForeignExchangeRatesNetOfContributionsReceived_019e92e9-54be-7036-acaa-679272771351" xlink:href="xndu-20260630.xsd#xndu_LongTermDebtIncreaseDecreaseInForeignExchangeRatesNetOfContributionsReceived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ReconciliationOfCarryingValueOfLoansRollForward_019e92e9-54be-7af1-b4ff-682d95d3f419" xlink:to="loc_xndu_LongTermDebtIncreaseDecreaseInForeignExchangeRatesNetOfContributionsReceived_019e92e9-54be-7036-acaa-679272771351" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_InterestExpenseNetOfForeignExchangeRatesDebt_019e92e9-54be-7211-aee5-d4b3a18dc383" xlink:href="xndu-20260630.xsd#xndu_InterestExpenseNetOfForeignExchangeRatesDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ReconciliationOfCarryingValueOfLoansRollForward_019e92e9-54be-7af1-b4ff-682d95d3f419" xlink:to="loc_xndu_InterestExpenseNetOfForeignExchangeRatesDebt_019e92e9-54be-7211-aee5-d4b3a18dc383" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019e92e9-54be-7485-9915-03ca8724c735" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebt"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/WarrantLiabilitiesScheduleofWarrantLiabilitiesDetails" xlink:type="simple" xlink:href="xndu-20260630.xsd#WarrantLiabilitiesScheduleofWarrantLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/WarrantLiabilitiesScheduleofWarrantLiabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightLineItems_019e92e9-54be-77bd-abb0-ce4fbaea6366" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightTable_019e92e9-54be-7d7b-b3dd-75da121e0028" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019e92e9-54be-77bd-abb0-ce4fbaea6366" xlink:to="loc_us-gaap_ClassOfWarrantOrRightTable_019e92e9-54be-7d7b-b3dd-75da121e0028" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_019e92e9-54be-73b0-98bf-714b9095043d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfWarrantOrRightTable_019e92e9-54be-7d7b-b3dd-75da121e0028" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_019e92e9-54be-73b0-98bf-714b9095043d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019e92e9-54be-73b0-98bf-714b9095043d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019e92e9-54be-73b0-98bf-714b9095043d" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019e92e9-54be-73b0-98bf-714b9095043d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019e92e9-54be-735a-a31a-57cb3b55b7f4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019e92e9-54be-73b0-98bf-714b9095043d" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019e92e9-54be-735a-a31a-57cb3b55b7f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_MVSWarrantsMember_019e92e9-54be-7178-ba49-1ebb428c7131" xlink:href="xndu-20260630.xsd#xndu_MVSWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019e92e9-54be-735a-a31a-57cb3b55b7f4" xlink:to="loc_xndu_MVSWarrantsMember_019e92e9-54be-7178-ba49-1ebb428c7131" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_SVSWarrantsMember_019e92e9-54be-72be-b73b-060b929f28cd" xlink:href="xndu-20260630.xsd#xndu_SVSWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019e92e9-54be-735a-a31a-57cb3b55b7f4" xlink:to="loc_xndu_SVSWarrantsMember_019e92e9-54be-72be-b73b-060b929f28cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantsAndRightsOutstanding_019e92e9-54be-7d1e-bb93-edf4f72c370c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantsAndRightsOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019e92e9-54be-77bd-abb0-ce4fbaea6366" xlink:to="loc_us-gaap_WarrantsAndRightsOutstanding_019e92e9-54be-7d1e-bb93-edf4f72c370c" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/WarrantLiabilitiesNarrativeDetails" xlink:type="simple" xlink:href="xndu-20260630.xsd#WarrantLiabilitiesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/WarrantLiabilitiesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightLineItems_019f6548-8d6b-726f-8479-4017c20cd239" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightTable_019e92e9-54be-7f4d-b6e2-3ca12d0d902c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019f6548-8d6b-726f-8479-4017c20cd239" xlink:to="loc_us-gaap_ClassOfWarrantOrRightTable_019e92e9-54be-7f4d-b6e2-3ca12d0d902c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByLiabilityClassAxis_019f6548-8d6b-7698-8708-410b64fbcab6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByLiabilityClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfWarrantOrRightTable_019e92e9-54be-7f4d-b6e2-3ca12d0d902c" xlink:to="loc_us-gaap_FairValueByLiabilityClassAxis_019f6548-8d6b-7698-8708-410b64fbcab6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019f6548-8d6b-7698-8708-410b64fbcab6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_019f6548-8d6b-7698-8708-410b64fbcab6" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019f6548-8d6b-7698-8708-410b64fbcab6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019f6548-8d6b-72b9-8e34-1e47f520593e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_019f6548-8d6b-7698-8708-410b64fbcab6" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019f6548-8d6b-72b9-8e34-1e47f520593e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_WarrantLiabilityMember_019f6548-8d6b-724e-8c52-de8c8b73b8ec" xlink:href="xndu-20260630.xsd#xndu_WarrantLiabilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019f6548-8d6b-72b9-8e34-1e47f520593e" xlink:to="loc_xndu_WarrantLiabilityMember_019f6548-8d6b-724e-8c52-de8c8b73b8ec" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019f6548-8d6b-7285-8321-ffffdd1574fb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfWarrantOrRightTable_019e92e9-54be-7f4d-b6e2-3ca12d0d902c" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019f6548-8d6b-7285-8321-ffffdd1574fb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019f6548-8d6b-7285-8321-ffffdd1574fb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019f6548-8d6b-7285-8321-ffffdd1574fb" xlink:to="loc_us-gaap_EquityComponentDomain_019f6548-8d6b-7285-8321-ffffdd1574fb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019f6548-8d6b-708b-942a-b0204bc5dee2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019f6548-8d6b-7285-8321-ffffdd1574fb" xlink:to="loc_us-gaap_EquityComponentDomain_019f6548-8d6b-708b-942a-b0204bc5dee2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019f6548-8d6b-71e5-b615-70fbf8df66e9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019f6548-8d6b-708b-942a-b0204bc5dee2" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019f6548-8d6b-71e5-b615-70fbf8df66e9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_019f6548-8d6b-7b67-81b8-b3a5c35c8951" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfWarrantOrRightTable_019e92e9-54be-7f4d-b6e2-3ca12d0d902c" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_019f6548-8d6b-7b67-81b8-b3a5c35c8951" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019f6548-8d6b-7b67-81b8-b3a5c35c8951_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019f6548-8d6b-7b67-81b8-b3a5c35c8951" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019f6548-8d6b-7b67-81b8-b3a5c35c8951_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019f6548-8d6b-7311-8148-63e5663cf9a1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019f6548-8d6b-7b67-81b8-b3a5c35c8951" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019f6548-8d6b-7311-8148-63e5663cf9a1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_SFTrustWarrantsMember_019f6548-8d6b-7c54-b449-a2b0e3ecf72c" xlink:href="xndu-20260630.xsd#xndu_SFTrustWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019f6548-8d6b-7311-8148-63e5663cf9a1" xlink:to="loc_xndu_SFTrustWarrantsMember_019f6548-8d6b-7c54-b449-a2b0e3ecf72c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_MVSWarrantsMember_019f6548-c536-74d3-9604-fa49dc4749d8" xlink:href="xndu-20260630.xsd#xndu_MVSWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019f6548-8d6b-7311-8148-63e5663cf9a1" xlink:to="loc_xndu_MVSWarrantsMember_019f6548-c536-74d3-9604-fa49dc4749d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_RBCWarrantsMember_019f6548-c536-72b0-8ee9-ca18b5b7a31f" xlink:href="xndu-20260630.xsd#xndu_RBCWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019f6548-8d6b-7311-8148-63e5663cf9a1" xlink:to="loc_xndu_RBCWarrantsMember_019f6548-c536-72b0-8ee9-ca18b5b7a31f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_SVSWarrantsMember_019f6548-c536-7b5c-9b8e-28d4bdb3c343" xlink:href="xndu-20260630.xsd#xndu_SVSWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019f6548-8d6b-7311-8148-63e5663cf9a1" xlink:to="loc_xndu_SVSWarrantsMember_019f6548-c536-7b5c-9b8e-28d4bdb3c343" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ReverseRecapitalizationWarrantExchangeComponentAxis_019f6548-c536-7348-98e7-27205e6bc3e5" xlink:href="xndu-20260630.xsd#xndu_ReverseRecapitalizationWarrantExchangeComponentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfWarrantOrRightTable_019e92e9-54be-7f4d-b6e2-3ca12d0d902c" xlink:to="loc_xndu_ReverseRecapitalizationWarrantExchangeComponentAxis_019f6548-c536-7348-98e7-27205e6bc3e5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ReverseRecapitalizationWarrantExchangeComponentDomain_019f6548-c536-7348-98e7-27205e6bc3e5_default" xlink:href="xndu-20260630.xsd#xndu_ReverseRecapitalizationWarrantExchangeComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_xndu_ReverseRecapitalizationWarrantExchangeComponentAxis_019f6548-c536-7348-98e7-27205e6bc3e5" xlink:to="loc_xndu_ReverseRecapitalizationWarrantExchangeComponentDomain_019f6548-c536-7348-98e7-27205e6bc3e5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ReverseRecapitalizationWarrantExchangeComponentDomain_019f6548-c536-78c9-9d97-fe331955fe6c" xlink:href="xndu-20260630.xsd#xndu_ReverseRecapitalizationWarrantExchangeComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_xndu_ReverseRecapitalizationWarrantExchangeComponentAxis_019f6548-c536-7348-98e7-27205e6bc3e5" xlink:to="loc_xndu_ReverseRecapitalizationWarrantExchangeComponentDomain_019f6548-c536-78c9-9d97-fe331955fe6c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_WarrantExchangeComponentOneMember_019f6548-c536-7f07-a910-8ea80caedabe" xlink:href="xndu-20260630.xsd#xndu_WarrantExchangeComponentOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ReverseRecapitalizationWarrantExchangeComponentDomain_019f6548-c536-78c9-9d97-fe331955fe6c" xlink:to="loc_xndu_WarrantExchangeComponentOneMember_019f6548-c536-7f07-a910-8ea80caedabe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_WarrantExchangeComponentTwoMember_019f6548-c536-7610-9f9b-7a69402dfc97" xlink:href="xndu-20260630.xsd#xndu_WarrantExchangeComponentTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_xndu_ReverseRecapitalizationWarrantExchangeComponentDomain_019f6548-c536-78c9-9d97-fe331955fe6c" xlink:to="loc_xndu_WarrantExchangeComponentTwoMember_019f6548-c536-7610-9f9b-7a69402dfc97" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019f6548-c536-7a52-9000-6aaea288673e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfWarrantOrRightTable_019e92e9-54be-7f4d-b6e2-3ca12d0d902c" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019f6548-c536-7a52-9000-6aaea288673e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019f6548-c536-7a52-9000-6aaea288673e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019f6548-c536-7a52-9000-6aaea288673e" xlink:to="loc_us-gaap_ClassOfStockDomain_019f6548-c536-7a52-9000-6aaea288673e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019f6548-c536-7f5b-9168-0eb09c6524e6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019f6548-c536-7a52-9000-6aaea288673e" xlink:to="loc_us-gaap_ClassOfStockDomain_019f6548-c536-7f5b-9168-0eb09c6524e6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_XanaduClassAMultipleVotingSharesMember_019f6548-c536-7864-ae06-128dd8c5bb39" xlink:href="xndu-20260630.xsd#xndu_XanaduClassAMultipleVotingSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019f6548-c536-7f5b-9168-0eb09c6524e6" xlink:to="loc_xndu_XanaduClassAMultipleVotingSharesMember_019f6548-c536-7864-ae06-128dd8c5bb39" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_XanaduClassBSubordinateVotingSharesEarnOutSharesMember_019f6548-c536-7996-a654-b33c9abc7257" xlink:href="xndu-20260630.xsd#xndu_XanaduClassBSubordinateVotingSharesEarnOutSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019f6548-c536-7f5b-9168-0eb09c6524e6" xlink:to="loc_xndu_XanaduClassBSubordinateVotingSharesEarnOutSharesMember_019f6548-c536-7996-a654-b33c9abc7257" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019f6548-c536-7e04-87fa-52b13e878c23" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfWarrantOrRightTable_019e92e9-54be-7f4d-b6e2-3ca12d0d902c" xlink:to="loc_us-gaap_DebtInstrumentAxis_019f6548-c536-7e04-87fa-52b13e878c23" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019f6548-c536-7e04-87fa-52b13e878c23_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019f6548-c536-7e04-87fa-52b13e878c23" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019f6548-c536-7e04-87fa-52b13e878c23_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019f6548-c536-7bac-abf3-f6f47a3aa0c0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019f6548-c536-7e04-87fa-52b13e878c23" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019f6548-c536-7bac-abf3-f6f47a3aa0c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_RBCTermLoanMember_019f6548-c536-7c26-9f5a-53de62540b76" xlink:href="xndu-20260630.xsd#xndu_RBCTermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019f6548-c536-7bac-abf3-f6f47a3aa0c0" xlink:to="loc_xndu_RBCTermLoanMember_019f6548-c536-7c26-9f5a-53de62540b76" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAdjustmentOfWarrants_019f6548-8d6b-7365-993d-e758d7a2e28d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAdjustmentOfWarrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019f6548-8d6b-726f-8479-4017c20cd239" xlink:to="loc_us-gaap_FairValueAdjustmentOfWarrants_019f6548-8d6b-7365-993d-e758d7a2e28d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued_019f6548-8d6b-71a6-b70e-a936f81661e3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019f6548-8d6b-726f-8479-4017c20cd239" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued_019f6548-8d6b-71a6-b70e-a936f81661e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightOutstanding_019f6548-8d6b-798a-9246-3d7b4a884713" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019f6548-8d6b-726f-8479-4017c20cd239" xlink:to="loc_us-gaap_ClassOfWarrantOrRightOutstanding_019f6548-8d6b-798a-9246-3d7b4a884713" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019f6548-8d6b-7d70-92db-0df5107e16d9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019f6548-8d6b-726f-8479-4017c20cd239" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019f6548-8d6b-7d70-92db-0df5107e16d9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantsAndRightsOutstandingTerm_019f6548-8d6b-7a14-9933-8821a67c8e9e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantsAndRightsOutstandingTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019f6548-8d6b-726f-8479-4017c20cd239" xlink:to="loc_us-gaap_WarrantsAndRightsOutstandingTerm_019f6548-8d6b-7a14-9933-8821a67c8e9e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019f6548-8d6b-7f54-996f-d26395f72c8b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019f6548-8d6b-726f-8479-4017c20cd239" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019f6548-8d6b-7f54-996f-d26395f72c8b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ClassOfWarrantsOrRightsVotingEquityInterestAcquiredPercentage_019f6548-8d6b-7ee4-a47d-c9d25a3fc4de" xlink:href="xndu-20260630.xsd#xndu_ClassOfWarrantsOrRightsVotingEquityInterestAcquiredPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019f6548-8d6b-726f-8479-4017c20cd239" xlink:to="loc_xndu_ClassOfWarrantsOrRightsVotingEquityInterestAcquiredPercentage_019f6548-8d6b-7ee4-a47d-c9d25a3fc4de" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ClassOfWarrantOrRightRedemptionTermLoanDrawTrigger_019f6548-8d6b-72ad-936f-036b75362421" xlink:href="xndu-20260630.xsd#xndu_ClassOfWarrantOrRightRedemptionTermLoanDrawTrigger"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019f6548-8d6b-726f-8479-4017c20cd239" xlink:to="loc_xndu_ClassOfWarrantOrRightRedemptionTermLoanDrawTrigger_019f6548-8d6b-72ad-936f-036b75362421" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ClassOfWarrantsAndRightsVestedInPeriod_019f6548-8d6b-7bd6-98db-0051348bd144" xlink:href="xndu-20260630.xsd#xndu_ClassOfWarrantsAndRightsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019f6548-8d6b-726f-8479-4017c20cd239" xlink:to="loc_xndu_ClassOfWarrantsAndRightsVestedInPeriod_019f6548-8d6b-7bd6-98db-0051348bd144" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ClassOfWarrantsAndRightsExpiredInPeriod_019f6548-8d6b-7e30-8629-b6f6bae35355" xlink:href="xndu-20260630.xsd#xndu_ClassOfWarrantsAndRightsExpiredInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019f6548-8d6b-726f-8479-4017c20cd239" xlink:to="loc_xndu_ClassOfWarrantsAndRightsExpiredInPeriod_019f6548-8d6b-7e30-8629-b6f6bae35355" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ClassOfWarrantOrRightNumberOfWarrantsSurrenderedToCoverExercisePrice_019f6548-c536-7d59-b2a9-2699ab1bbbf9" xlink:href="xndu-20260630.xsd#xndu_ClassOfWarrantOrRightNumberOfWarrantsSurrenderedToCoverExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019f6548-8d6b-726f-8479-4017c20cd239" xlink:to="loc_xndu_ClassOfWarrantOrRightNumberOfWarrantsSurrenderedToCoverExercisePrice_019f6548-c536-7d59-b2a9-2699ab1bbbf9" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantsAndRightsOutstanding_019f6548-c536-7be9-b569-527273e8d853" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantsAndRightsOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019f6548-8d6b-726f-8479-4017c20cd239" xlink:to="loc_us-gaap_WarrantsAndRightsOutstanding_019f6548-c536-7be9-b569-527273e8d853" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_019f6548-c536-752c-81ed-728a97b3cded" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019f6548-8d6b-726f-8479-4017c20cd239" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_019f6548-c536-752c-81ed-728a97b3cded" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/FairValueMeasurementScheduleofCarryingAmountsandFairValuesDetails" xlink:type="simple" xlink:href="xndu-20260630.xsd#FairValueMeasurementScheduleofCarryingAmountsandFairValuesDetails"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/FairValueMeasurementScheduleofCarryingAmountsandFairValuesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019e92e9-54be-76d8-8d56-2f2cf75f9119" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019e92e9-54be-74f8-a792-62b7210484cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByBalanceSheetGroupingTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019e92e9-54be-76d8-8d56-2f2cf75f9119" xlink:to="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019e92e9-54be-74f8-a792-62b7210484cc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e92e9-54be-7677-a055-1e3181ba69d3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019e92e9-54be-74f8-a792-62b7210484cc" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e92e9-54be-7677-a055-1e3181ba69d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e92e9-54be-7677-a055-1e3181ba69d3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e92e9-54be-7677-a055-1e3181ba69d3" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e92e9-54be-7677-a055-1e3181ba69d3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e92e9-54be-7c25-9eba-2b6e813d73cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e92e9-54be-7677-a055-1e3181ba69d3" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e92e9-54be-7c25-9eba-2b6e813d73cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019e92e9-54be-73ae-ab21-fdb4ba6ca550" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e92e9-54be-7c25-9eba-2b6e813d73cb" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019e92e9-54be-73ae-ab21-fdb4ba6ca550" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019e92e9-54be-7ebf-969c-08de6b179e42" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e92e9-54be-7c25-9eba-2b6e813d73cb" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019e92e9-54be-7ebf-969c-08de6b179e42" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_019e92e9-54be-7d6f-b7e0-84eecc26c460" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019e92e9-54be-74f8-a792-62b7210484cc" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_019e92e9-54be-7d6f-b7e0-84eecc26c460" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019e92e9-54be-7d6f-b7e0-84eecc26c460_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019e92e9-54be-7d6f-b7e0-84eecc26c460" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019e92e9-54be-7d6f-b7e0-84eecc26c460_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019e92e9-54be-7792-8953-8155e26a738c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019e92e9-54be-7d6f-b7e0-84eecc26c460" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019e92e9-54be-7792-8953-8155e26a738c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019e92e9-54be-77b3-8e77-a222fe3e78b5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019e92e9-54be-7792-8953-8155e26a738c" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019e92e9-54be-77b3-8e77-a222fe3e78b5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019e92e9-54be-75f3-b398-36d1115bb7c4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019e92e9-54be-77b3-8e77-a222fe3e78b5" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019e92e9-54be-75f3-b398-36d1115bb7c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_019e92e9-54be-7591-8b28-9f1c199d4b2d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019e92e9-54be-77b3-8e77-a222fe3e78b5" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_019e92e9-54be-7591-8b28-9f1c199d4b2d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019e92e9-54be-7529-a807-e7799418c2d1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019e92e9-54be-74f8-a792-62b7210484cc" xlink:to="loc_us-gaap_DebtInstrumentAxis_019e92e9-54be-7529-a807-e7799418c2d1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019e92e9-54be-7529-a807-e7799418c2d1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019e92e9-54be-7529-a807-e7799418c2d1" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019e92e9-54be-7529-a807-e7799418c2d1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019e92e9-54be-740b-aadc-8619a2f00ee3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019e92e9-54be-7529-a807-e7799418c2d1" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019e92e9-54be-740b-aadc-8619a2f00ee3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_SIFLoanMember_019e92e9-54be-7038-9322-afd7e92e13e8" xlink:href="xndu-20260630.xsd#xndu_SIFLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e92e9-54be-740b-aadc-8619a2f00ee3" xlink:to="loc_xndu_SIFLoanMember_019e92e9-54be-7038-9322-afd7e92e13e8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_FedDevLoanMember_019e92e9-54be-724e-9c48-e6a567e5e791" xlink:href="xndu-20260630.xsd#xndu_FedDevLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e92e9-54be-740b-aadc-8619a2f00ee3" xlink:to="loc_xndu_FedDevLoanMember_019e92e9-54be-724e-9c48-e6a567e5e791" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantsAndRightsOutstanding_019e92e9-54be-7e42-8d54-844d0efe7e92" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantsAndRightsOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019e92e9-54be-76d8-8d56-2f2cf75f9119" xlink:to="loc_us-gaap_WarrantsAndRightsOutstanding_019e92e9-54be-7e42-8d54-844d0efe7e92" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtFairValue_019e92e9-54be-7f30-84d4-d3a582168910" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019e92e9-54be-76d8-8d56-2f2cf75f9119" xlink:to="loc_us-gaap_LongTermDebtFairValue_019e92e9-54be-7f30-84d4-d3a582168910" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetsCurrent_019fb1a1-394f-7823-8608-60f8546206ca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019e92e9-54be-76d8-8d56-2f2cf75f9119" xlink:to="loc_us-gaap_DerivativeAssetsCurrent_019fb1a1-394f-7823-8608-60f8546206ca" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/FairValueMeasurementScheduleofReconciliationofChangesinFairValueDetails" xlink:type="simple" xlink:href="xndu-20260630.xsd#FairValueMeasurementScheduleofReconciliationofChangesinFairValueDetails"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/FairValueMeasurementScheduleofReconciliationofChangesinFairValueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019e92e9-54be-7172-9207-5fe40fc804ca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019e92e9-54be-7a21-8dd7-b4b87c40fc78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019e92e9-54be-7172-9207-5fe40fc804ca" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019e92e9-54be-7a21-8dd7-b4b87c40fc78" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByLiabilityClassAxis_019e92e9-54be-7736-ad15-15c91dcc92e1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByLiabilityClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019e92e9-54be-7a21-8dd7-b4b87c40fc78" xlink:to="loc_us-gaap_FairValueByLiabilityClassAxis_019e92e9-54be-7736-ad15-15c91dcc92e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019e92e9-54be-7736-ad15-15c91dcc92e1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_019e92e9-54be-7736-ad15-15c91dcc92e1" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019e92e9-54be-7736-ad15-15c91dcc92e1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019e92e9-54be-7448-87be-58f4d3f582fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_019e92e9-54be-7736-ad15-15c91dcc92e1" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019e92e9-54be-7448-87be-58f4d3f582fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_WarrantLiabilityMember_019e92e9-54be-7858-bd25-1d7649c7101a" xlink:href="xndu-20260630.xsd#xndu_WarrantLiabilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019e92e9-54be-7448-87be-58f4d3f582fe" xlink:to="loc_xndu_WarrantLiabilityMember_019e92e9-54be-7858-bd25-1d7649c7101a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember_019e92e9-54be-74f6-82c5-3b3b183bcc9d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019e92e9-54be-7448-87be-58f4d3f582fe" xlink:to="loc_us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember_019e92e9-54be-74f6-82c5-3b3b183bcc9d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFinancialInstrumentsAssetsMember_019fb346-3cc1-7c9a-ac01-e81498400ed4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeFinancialInstrumentsAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019e92e9-54be-7448-87be-58f4d3f582fe" xlink:to="loc_us-gaap_DerivativeFinancialInstrumentsAssetsMember_019fb346-3cc1-7c9a-ac01-e81498400ed4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019e92e9-54be-7a23-bb25-05b2bee656fd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019e92e9-54be-7172-9207-5fe40fc804ca" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019e92e9-54be-7a23-bb25-05b2bee656fd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_019e92e9-54be-7d3a-a774-d193316053a5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019e92e9-54be-7a23-bb25-05b2bee656fd" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_019e92e9-54be-7d3a-a774-d193316053a5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIssues_019e92e9-54be-7b49-b80a-3a11c7869f25" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019e92e9-54be-7a23-bb25-05b2bee656fd" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIssues_019e92e9-54be-7b49-b80a-3a11c7869f25" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings_019e92e9-54be-77cb-92cd-824118e58b52" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019e92e9-54be-7a23-bb25-05b2bee656fd" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings_019e92e9-54be-77cb-92cd-824118e58b52" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityReclassificationOfLiabilityToEquity_019e92e9-54be-7bf3-af7b-83dd0bd421a4" xlink:href="xndu-20260630.xsd#xndu_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityReclassificationOfLiabilityToEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019e92e9-54be-7a23-bb25-05b2bee656fd" xlink:to="loc_xndu_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityReclassificationOfLiabilityToEquity_019e92e9-54be-7bf3-af7b-83dd0bd421a4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_019e92e9-54be-7af8-84bf-8dd0a1413f3d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLossOnDerivative_019fb1b9-79df-7ed1-8e3c-81f3692a294c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLossOnDerivative"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019e92e9-54be-7172-9207-5fe40fc804ca" xlink:to="loc_us-gaap_DerivativeLossOnDerivative_019fb1b9-79df-7ed1-8e3c-81f3692a294c" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/FairValueMeasurementScheduleofFairValueMeasurementInputsDetails" xlink:type="simple" xlink:href="xndu-20260630.xsd#FairValueMeasurementScheduleofFairValueMeasurementInputsDetails"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/FairValueMeasurementScheduleofFairValueMeasurementInputsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019e92e9-54be-7c8c-840d-a33c4b55eb01" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019e92e9-54be-7bf1-9d0e-050bbc24c370" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019e92e9-54be-7c8c-840d-a33c4b55eb01" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019e92e9-54be-7bf1-9d0e-050bbc24c370" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_019e92e9-54be-7003-9db9-0df8ef2fc6ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019e92e9-54be-7bf1-9d0e-050bbc24c370" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_019e92e9-54be-7003-9db9-0df8ef2fc6ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019e92e9-54be-7003-9db9-0df8ef2fc6ff_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_019e92e9-54be-7003-9db9-0df8ef2fc6ff" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019e92e9-54be-7003-9db9-0df8ef2fc6ff_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019e92e9-54be-72dc-a970-6b7556fe169a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_019e92e9-54be-7003-9db9-0df8ef2fc6ff" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019e92e9-54be-72dc-a970-6b7556fe169a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_MeasurementInputSharesSubjectToFairValueMember_019f25ea-a49d-70b3-a43e-50463ddc955e" xlink:href="xndu-20260630.xsd#xndu_MeasurementInputSharesSubjectToFairValueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019e92e9-54be-72dc-a970-6b7556fe169a" xlink:to="loc_xndu_MeasurementInputSharesSubjectToFairValueMember_019f25ea-a49d-70b3-a43e-50463ddc955e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputSharePriceMember_019e92e9-54be-70d2-be96-d3d654134b59" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputSharePriceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019e92e9-54be-72dc-a970-6b7556fe169a" xlink:to="loc_us-gaap_MeasurementInputSharePriceMember_019e92e9-54be-70d2-be96-d3d654134b59" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputPriceVolatilityMember_019e92e9-54be-7f4d-9beb-a357bc77fbad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputPriceVolatilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019e92e9-54be-72dc-a970-6b7556fe169a" xlink:to="loc_us-gaap_MeasurementInputPriceVolatilityMember_019e92e9-54be-7f4d-9beb-a357bc77fbad" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputRiskFreeInterestRateMember_019e92e9-54be-7a8a-aeb8-096edc836428" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputRiskFreeInterestRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019e92e9-54be-72dc-a970-6b7556fe169a" xlink:to="loc_us-gaap_MeasurementInputRiskFreeInterestRateMember_019e92e9-54be-7a8a-aeb8-096edc836428" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputExpectedTermMember_019e92e9-54be-72a6-918f-9ceec90e3e72" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputExpectedTermMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019e92e9-54be-72dc-a970-6b7556fe169a" xlink:to="loc_us-gaap_MeasurementInputExpectedTermMember_019e92e9-54be-72a6-918f-9ceec90e3e72" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_MeasurementInputFairValueMember_019f25e9-bc52-7f7f-bc00-118c370aea9e" xlink:href="xndu-20260630.xsd#xndu_MeasurementInputFairValueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019e92e9-54be-72dc-a970-6b7556fe169a" xlink:to="loc_xndu_MeasurementInputFairValueMember_019f25e9-bc52-7f7f-bc00-118c370aea9e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e92e9-54be-7778-abbf-584ee43a6a4e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019e92e9-54be-7bf1-9d0e-050bbc24c370" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e92e9-54be-7778-abbf-584ee43a6a4e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e92e9-54be-7778-abbf-584ee43a6a4e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e92e9-54be-7778-abbf-584ee43a6a4e" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e92e9-54be-7778-abbf-584ee43a6a4e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e92e9-54be-78d3-8a14-6cf0a4f534c3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e92e9-54be-7778-abbf-584ee43a6a4e" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e92e9-54be-78d3-8a14-6cf0a4f534c3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019e92e9-54be-758b-bc00-75ced53a7dbf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e92e9-54be-78d3-8a14-6cf0a4f534c3" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019e92e9-54be-758b-bc00-75ced53a7dbf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilityMeasurementInput_019e92e9-54be-7764-8b6f-ed33410c8e82" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLiabilityMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019e92e9-54be-7c8c-840d-a33c4b55eb01" xlink:to="loc_us-gaap_DerivativeLiabilityMeasurementInput_019e92e9-54be-7764-8b6f-ed33410c8e82" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_DerivativeInstrumentForfeitureHurdleSharePriceAchieved_019fa7ab-d2dd-7fbc-9289-f099e57fd56e" xlink:href="xndu-20260630.xsd#xndu_DerivativeInstrumentForfeitureHurdleSharePriceAchieved"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019e92e9-54be-7c8c-840d-a33c4b55eb01" xlink:to="loc_xndu_DerivativeInstrumentForfeitureHurdleSharePriceAchieved_019fa7ab-d2dd-7fbc-9289-f099e57fd56e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_DerivativeInstrumentMaximumForfeitureHurdleSharePrice_019fa7ab-d2dd-7c6b-b77b-e457fd15579c" xlink:href="xndu-20260630.xsd#xndu_DerivativeInstrumentMaximumForfeitureHurdleSharePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019e92e9-54be-7c8c-840d-a33c4b55eb01" xlink:to="loc_xndu_DerivativeInstrumentMaximumForfeitureHurdleSharePrice_019fa7ab-d2dd-7c6b-b77b-e457fd15579c" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/RevenueRecognitionScheduleofDisaggregationofRevenueDetails" xlink:type="simple" xlink:href="xndu-20260630.xsd#RevenueRecognitionScheduleofDisaggregationofRevenueDetails"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/RevenueRecognitionScheduleofDisaggregationofRevenueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-54be-7491-bce8-9ce57ea1489c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_019e92e9-54be-720e-825b-0a180adc955a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-54be-7491-bce8-9ce57ea1489c" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_019e92e9-54be-720e-825b-0a180adc955a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019e92e9-54be-7615-93a8-81d1572860d4" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019e92e9-54be-720e-825b-0a180adc955a" xlink:to="loc_srt_ProductOrServiceAxis_019e92e9-54be-7615-93a8-81d1572860d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019e92e9-54be-7615-93a8-81d1572860d4_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019e92e9-54be-7615-93a8-81d1572860d4" xlink:to="loc_srt_ProductsAndServicesDomain_019e92e9-54be-7615-93a8-81d1572860d4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019e92e9-54be-7a73-8beb-12657550fc8a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019e92e9-54be-7615-93a8-81d1572860d4" xlink:to="loc_srt_ProductsAndServicesDomain_019e92e9-54be-7a73-8beb-12657550fc8a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ProfessionalServicesMember_019e92e9-54be-7d8b-965c-92461d1153a8" xlink:href="xndu-20260630.xsd#xndu_ProfessionalServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019e92e9-54be-7a73-8beb-12657550fc8a" xlink:to="loc_xndu_ProfessionalServicesMember_019e92e9-54be-7d8b-965c-92461d1153a8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ComputeAndOtherServicesMember_019e92e9-54be-7c94-9671-baf7230608d4" xlink:href="xndu-20260630.xsd#xndu_ComputeAndOtherServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019e92e9-54be-7a73-8beb-12657550fc8a" xlink:to="loc_xndu_ComputeAndOtherServicesMember_019e92e9-54be-7c94-9671-baf7230608d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e92e9-54be-7c2b-a152-1b71ad905af9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-54be-7491-bce8-9ce57ea1489c" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e92e9-54be-7c2b-a152-1b71ad905af9" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/RevenueRecognitionScheduleofRevenuebyGeographyDetails" xlink:type="simple" xlink:href="xndu-20260630.xsd#RevenueRecognitionScheduleofRevenuebyGeographyDetails"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/RevenueRecognitionScheduleofRevenuebyGeographyDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-54be-7519-a22f-bdc11c1b5292" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_019e92e9-54be-733b-88e0-b1187a25bc6a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-54be-7519-a22f-bdc11c1b5292" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_019e92e9-54be-733b-88e0-b1187a25bc6a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_019e92e9-54be-723e-902e-e8ea4ec598eb" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019e92e9-54be-733b-88e0-b1187a25bc6a" xlink:to="loc_srt_StatementGeographicalAxis_019e92e9-54be-723e-902e-e8ea4ec598eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019e92e9-54be-723e-902e-e8ea4ec598eb_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_019e92e9-54be-723e-902e-e8ea4ec598eb" xlink:to="loc_srt_SegmentGeographicalDomain_019e92e9-54be-723e-902e-e8ea4ec598eb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019e92e9-54be-72e3-903f-7c61be34ff47" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_019e92e9-54be-723e-902e-e8ea4ec598eb" xlink:to="loc_srt_SegmentGeographicalDomain_019e92e9-54be-72e3-903f-7c61be34ff47" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_CA_019e92e9-54be-7337-8cb1-aa9754c54823" xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_CA"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019e92e9-54be-72e3-903f-7c61be34ff47" xlink:to="loc_country_CA_019e92e9-54be-7337-8cb1-aa9754c54823" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_019e92e9-54be-770a-8f10-ed3474e8b5df" xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019e92e9-54be-72e3-903f-7c61be34ff47" xlink:to="loc_country_US_019e92e9-54be-770a-8f10-ed3474e8b5df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_RestOfWorldMember_019e92e9-54be-740e-8b56-ce12fc7eab09" xlink:href="xndu-20260630.xsd#xndu_RestOfWorldMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019e92e9-54be-72e3-903f-7c61be34ff47" xlink:to="loc_xndu_RestOfWorldMember_019e92e9-54be-740e-8b56-ce12fc7eab09" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e92e9-54be-7870-bb7d-16d303bd917a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-54be-7519-a22f-bdc11c1b5292" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e92e9-54be-7870-bb7d-16d303bd917a" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/RevenueRecognitionNarrativeDetails" xlink:type="simple" xlink:href="xndu-20260630.xsd#RevenueRecognitionNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/RevenueRecognitionNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-54be-7d20-b6a5-19f0ad5341cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_019e92e9-54be-72ab-9b9d-c151447f5211" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-54be-7d20-b6a5-19f0ad5341cc" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_019e92e9-54be-72ab-9b9d-c151447f5211" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_019e92e9-54be-7c46-80d1-352bb5545bdb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019e92e9-54be-72ab-9b9d-c151447f5211" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_019e92e9-54be-7c46-80d1-352bb5545bdb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetNetCurrent_019e92e9-54be-7f6b-9b06-3d91f121da51" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerAssetNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-54be-7d20-b6a5-19f0ad5341cc" xlink:to="loc_us-gaap_ContractWithCustomerAssetNetCurrent_019e92e9-54be-7f6b-9b06-3d91f121da51" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_019e92e9-54be-774c-ac94-fcd9f2775d9d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-54be-7d20-b6a5-19f0ad5341cc" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_019e92e9-54be-774c-ac94-fcd9f2775d9d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_019e92e9-54be-73ea-ade8-71843c227e7e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-54be-7d20-b6a5-19f0ad5341cc" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_019e92e9-54be-73ea-ade8-71843c227e7e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_019e92e9-54be-77a9-b6b7-5203f0a2a0d4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-54be-7d20-b6a5-19f0ad5341cc" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_019e92e9-54be-77a9-b6b7-5203f0a2a0d4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019e92e9-54be-72c9-8990-f1eaa0b30f47" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-54be-7d20-b6a5-19f0ad5341cc" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019e92e9-54be-72c9-8990-f1eaa0b30f47" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/RevenueRecognitionNarrativeDetails_1" xlink:type="simple" xlink:href="xndu-20260630.xsd#RevenueRecognitionNarrativeDetails_1"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/RevenueRecognitionNarrativeDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-54be-7d20-b6a5-19f0ad5341cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_019e92e9-54be-72ab-9b9d-c151447f5211" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-54be-7d20-b6a5-19f0ad5341cc" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_019e92e9-54be-72ab-9b9d-c151447f5211" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetNetCurrent_019e92e9-54be-7f6b-9b06-3d91f121da51" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerAssetNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-54be-7d20-b6a5-19f0ad5341cc" xlink:to="loc_us-gaap_ContractWithCustomerAssetNetCurrent_019e92e9-54be-7f6b-9b06-3d91f121da51" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_019e92e9-54be-774c-ac94-fcd9f2775d9d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-54be-7d20-b6a5-19f0ad5341cc" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_019e92e9-54be-774c-ac94-fcd9f2775d9d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_019e92e9-54be-73ea-ade8-71843c227e7e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-54be-7d20-b6a5-19f0ad5341cc" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_019e92e9-54be-73ea-ade8-71843c227e7e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_019e92e9-54be-77a9-b6b7-5203f0a2a0d4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-54be-7d20-b6a5-19f0ad5341cc" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_019e92e9-54be-77a9-b6b7-5203f0a2a0d4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019e92e9-54be-72c9-8990-f1eaa0b30f47" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e92e9-54be-7d20-b6a5-19f0ad5341cc" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019e92e9-54be-72c9-8990-f1eaa0b30f47" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/RevenueRecognitionScheduleofPercentageofRevenuefromSignificantCustomersDetails" xlink:type="simple" xlink:href="xndu-20260630.xsd#RevenueRecognitionScheduleofPercentageofRevenuefromSignificantCustomersDetails"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/RevenueRecognitionScheduleofPercentageofRevenuefromSignificantCustomersDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskLineItems_019e92e9-54be-7ca7-a22a-631fef777d03" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTable_019e92e9-54be-7970-897a-cf3ada55b639" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_019e92e9-54be-7ca7-a22a-631fef777d03" xlink:to="loc_us-gaap_ConcentrationRiskTable_019e92e9-54be-7970-897a-cf3ada55b639" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019e92e9-54be-7afa-9c43-7b94e5cba5a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_019e92e9-54be-7970-897a-cf3ada55b639" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019e92e9-54be-7afa-9c43-7b94e5cba5a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e92e9-54be-7afa-9c43-7b94e5cba5a8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019e92e9-54be-7afa-9c43-7b94e5cba5a8" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e92e9-54be-7afa-9c43-7b94e5cba5a8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e92e9-54be-7cac-9142-22910b75bd75" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019e92e9-54be-7afa-9c43-7b94e5cba5a8" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e92e9-54be-7cac-9142-22910b75bd75" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_019e92e9-54be-7321-8a2b-fe8283b94690" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e92e9-54be-7cac-9142-22910b75bd75" xlink:to="loc_us-gaap_SalesRevenueNetMember_019e92e9-54be-7321-8a2b-fe8283b94690" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_019e92e9-54be-7ce3-afb4-2a9bfc9cc8ce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_019e92e9-54be-7970-897a-cf3ada55b639" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_019e92e9-54be-7ce3-afb4-2a9bfc9cc8ce" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019e92e9-54be-7ce3-afb4-2a9bfc9cc8ce_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019e92e9-54be-7ce3-afb4-2a9bfc9cc8ce" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019e92e9-54be-7ce3-afb4-2a9bfc9cc8ce_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019e92e9-54be-7673-90b9-a0ae46f53db2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019e92e9-54be-7ce3-afb4-2a9bfc9cc8ce" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019e92e9-54be-7673-90b9-a0ae46f53db2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_019e92e9-54be-73c6-8df6-74380a09a82a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019e92e9-54be-7673-90b9-a0ae46f53db2" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_019e92e9-54be-73c6-8df6-74380a09a82a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_019e92e9-54be-7561-a33b-cb1cfc907c83" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_019e92e9-54be-7970-897a-cf3ada55b639" xlink:to="loc_srt_MajorCustomersAxis_019e92e9-54be-7561-a33b-cb1cfc907c83" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019e92e9-54be-7561-a33b-cb1cfc907c83_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_019e92e9-54be-7561-a33b-cb1cfc907c83" xlink:to="loc_srt_NameOfMajorCustomerDomain_019e92e9-54be-7561-a33b-cb1cfc907c83_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019e92e9-54be-7102-8ebc-17afe3db5409" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_019e92e9-54be-7561-a33b-cb1cfc907c83" xlink:to="loc_srt_NameOfMajorCustomerDomain_019e92e9-54be-7102-8ebc-17afe3db5409" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_Customer1Member_019e92e9-54be-7351-8933-fb2911dde0f9" xlink:href="xndu-20260630.xsd#xndu_Customer1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019e92e9-54be-7102-8ebc-17afe3db5409" xlink:to="loc_xndu_Customer1Member_019e92e9-54be-7351-8933-fb2911dde0f9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_Customer2Member_019e92e9-54be-7f1a-bac7-5427e28618e1" xlink:href="xndu-20260630.xsd#xndu_Customer2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019e92e9-54be-7102-8ebc-17afe3db5409" xlink:to="loc_xndu_Customer2Member_019e92e9-54be-7f1a-bac7-5427e28618e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_Customer3Member_019e92e9-54be-79cd-a758-a2e8a4aa092f" xlink:href="xndu-20260630.xsd#xndu_Customer3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019e92e9-54be-7102-8ebc-17afe3db5409" xlink:to="loc_xndu_Customer3Member_019e92e9-54be-79cd-a758-a2e8a4aa092f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_019e92e9-54be-71ed-b43d-c6fee08e29f5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_019e92e9-54be-7ca7-a22a-631fef777d03" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_019e92e9-54be-71ed-b43d-c6fee08e29f5" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/ShareholdersEquityNarrativeDetails" xlink:type="simple" xlink:href="xndu-20260630.xsd#ShareholdersEquityNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/ShareholdersEquityNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_019f6516-af58-7a88-8d76-8e0de54273ec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_019e92e9-54be-70a7-a8d2-5b15cac2a94e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_019f6516-af58-7a88-8d76-8e0de54273ec" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_019e92e9-54be-70a7-a8d2-5b15cac2a94e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019f6516-af58-76e4-bc42-4f0344e4e3a5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019e92e9-54be-70a7-a8d2-5b15cac2a94e" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019f6516-af58-76e4-bc42-4f0344e4e3a5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019f6516-af58-76e4-bc42-4f0344e4e3a5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019f6516-af58-76e4-bc42-4f0344e4e3a5" xlink:to="loc_us-gaap_ClassOfStockDomain_019f6516-af58-76e4-bc42-4f0344e4e3a5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019f6516-af58-7c66-877a-5310ed2c7fc4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019f6516-af58-76e4-bc42-4f0344e4e3a5" xlink:to="loc_us-gaap_ClassOfStockDomain_019f6516-af58-7c66-877a-5310ed2c7fc4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019f6516-af58-7eba-8154-b3b0a04e118f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019f6516-af58-7c66-877a-5310ed2c7fc4" xlink:to="loc_us-gaap_CommonClassAMember_019f6516-af58-7eba-8154-b3b0a04e118f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_019f6516-af58-78ba-833d-7a77e09ca9d3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019f6516-af58-7c66-877a-5310ed2c7fc4" xlink:to="loc_us-gaap_CommonClassBMember_019f6516-af58-78ba-833d-7a77e09ca9d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_XanaduClassBSubordinateVotingSharesEarnOutSharesMember_019f6516-d89f-75ab-8bee-2c107f8d47eb" xlink:href="xndu-20260630.xsd#xndu_XanaduClassBSubordinateVotingSharesEarnOutSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019f6516-af58-7c66-877a-5310ed2c7fc4" xlink:to="loc_xndu_XanaduClassBSubordinateVotingSharesEarnOutSharesMember_019f6516-d89f-75ab-8bee-2c107f8d47eb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019f6516-d89f-777d-af87-ba8300edfd1d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019e92e9-54be-70a7-a8d2-5b15cac2a94e" xlink:to="loc_srt_CounterpartyNameAxis_019f6516-d89f-777d-af87-ba8300edfd1d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019f6516-d89f-777d-af87-ba8300edfd1d_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019f6516-d89f-777d-af87-ba8300edfd1d" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019f6516-d89f-777d-af87-ba8300edfd1d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019f6516-d89f-7485-b698-6c52a5455dfb" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019f6516-d89f-777d-af87-ba8300edfd1d" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019f6516-d89f-7485-b698-6c52a5455dfb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_YorkvilleInvestorMember_019f6516-d89f-7585-9d33-d80c3d2d29e0" xlink:href="xndu-20260630.xsd#xndu_YorkvilleInvestorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019f6516-d89f-7485-b698-6c52a5455dfb" xlink:to="loc_xndu_YorkvilleInvestorMember_019f6516-d89f-7585-9d33-d80c3d2d29e0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_019f6516-f466-7f0e-85bf-a8c78381f075" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019e92e9-54be-70a7-a8d2-5b15cac2a94e" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_019f6516-f466-7f0e-85bf-a8c78381f075" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019f6516-f466-7f0e-85bf-a8c78381f075_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019f6516-f466-7f0e-85bf-a8c78381f075" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019f6516-f466-7f0e-85bf-a8c78381f075_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019f6516-f466-7bd8-b1aa-e79126e94822" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019f6516-f466-7f0e-85bf-a8c78381f075" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019f6516-f466-7bd8-b1aa-e79126e94822" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_SFTrustWarrantsMember_019f6516-f466-7ee6-ab28-79df23a538d4" xlink:href="xndu-20260630.xsd#xndu_SFTrustWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019f6516-f466-7bd8-b1aa-e79126e94822" xlink:to="loc_xndu_SFTrustWarrantsMember_019f6516-f466-7ee6-ab28-79df23a538d4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_SVSWarrantsMember_019f6516-f466-77c8-a75a-8b5662226909" xlink:href="xndu-20260630.xsd#xndu_SVSWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019f6516-f466-7bd8-b1aa-e79126e94822" xlink:to="loc_xndu_SVSWarrantsMember_019f6516-f466-77c8-a75a-8b5662226909" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019fb7bc-fef3-7762-a111-21ff9a7cc85d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019e92e9-54be-70a7-a8d2-5b15cac2a94e" xlink:to="loc_srt_RangeAxis_019fb7bc-fef3-7762-a111-21ff9a7cc85d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fb7bc-fef3-7762-a111-21ff9a7cc85d_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019fb7bc-fef3-7762-a111-21ff9a7cc85d" xlink:to="loc_srt_RangeMember_019fb7bc-fef3-7762-a111-21ff9a7cc85d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fb7bc-fef3-7a44-a28e-80cdf838dca2" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019fb7bc-fef3-7762-a111-21ff9a7cc85d" xlink:to="loc_srt_RangeMember_019fb7bc-fef3-7a44-a28e-80cdf838dca2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019fb7bc-fef3-7ae7-bdeb-652292bce44f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fb7bc-fef3-7a44-a28e-80cdf838dca2" xlink:to="loc_srt_MaximumMember_019fb7bc-fef3-7ae7-bdeb-652292bce44f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_019fc84f-87a8-7d73-8af0-09305c995f38" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019e92e9-54be-70a7-a8d2-5b15cac2a94e" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_019fc84f-87a8-7d73-8af0-09305c995f38" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019fc84f-87a8-7d73-8af0-09305c995f38_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019fc84f-87a8-7d73-8af0-09305c995f38" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019fc84f-87a8-7d73-8af0-09305c995f38_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019fc84f-87a8-760c-8404-13189b5fa5e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019fc84f-87a8-7d73-8af0-09305c995f38" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019fc84f-87a8-760c-8404-13189b5fa5e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_SATMFacilityMember_019fc84f-a7e7-7058-baa5-6a4a39c7b890" xlink:href="xndu-20260630.xsd#xndu_SATMFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019fc84f-87a8-760c-8404-13189b5fa5e0" xlink:to="loc_xndu_SATMFacilityMember_019fc84f-a7e7-7058-baa5-6a4a39c7b890" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrivatePlacementMember_019fc84f-c2c2-7259-b824-4b4de8ff611f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PrivatePlacementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019fc84f-87a8-760c-8404-13189b5fa5e0" xlink:to="loc_us-gaap_PrivatePlacementMember_019fc84f-c2c2-7259-b824-4b4de8ff611f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019fc868-061a-7f8f-8f19-3fc82512570b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019e92e9-54be-70a7-a8d2-5b15cac2a94e" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019fc868-061a-7f8f-8f19-3fc82512570b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019fc868-061a-7f8f-8f19-3fc82512570b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019fc868-061a-7f8f-8f19-3fc82512570b" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019fc868-061a-7f8f-8f19-3fc82512570b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019fc868-061a-731b-97a4-0923d44136ed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019fc868-061a-7f8f-8f19-3fc82512570b" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019fc868-061a-731b-97a4-0923d44136ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_SATMFacilityMember_019fc868-1681-7e4f-9cfb-6a8d8135addf" xlink:href="xndu-20260630.xsd#xndu_SATMFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fc868-061a-731b-97a4-0923d44136ed" xlink:to="loc_xndu_SATMFacilityMember_019fc868-1681-7e4f-9cfb-6a8d8135addf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_NumberOfClassesOfCommonShares_019f6516-af58-7695-b850-6e9187a827a2" xlink:href="xndu-20260630.xsd#xndu_NumberOfClassesOfCommonShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019f6516-af58-7a88-8d76-8e0de54273ec" xlink:to="loc_xndu_NumberOfClassesOfCommonShares_019f6516-af58-7695-b850-6e9187a827a2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_CommonStockNumberOfVotes_019f6516-af58-7bd6-98de-105b780af58f" xlink:href="xndu-20260630.xsd#xndu_CommonStockNumberOfVotes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019f6516-af58-7a88-8d76-8e0de54273ec" xlink:to="loc_xndu_CommonStockNumberOfVotes_019f6516-af58-7bd6-98de-105b780af58f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_CommonStockConvertibleConversionRatio_019f6516-af58-7cfe-8524-ea3e10b6e069" xlink:href="xndu-20260630.xsd#xndu_CommonStockConvertibleConversionRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019f6516-af58-7a88-8d76-8e0de54273ec" xlink:to="loc_xndu_CommonStockConvertibleConversionRatio_019f6516-af58-7cfe-8524-ea3e10b6e069" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_019f6516-d89f-7730-91a5-4f55166a67cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019f6516-af58-7a88-8d76-8e0de54273ec" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_019f6516-d89f-7730-91a5-4f55166a67cc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_019f6516-d89f-7dcc-aa9a-37f1b99f53ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019f6516-af58-7a88-8d76-8e0de54273ec" xlink:to="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_019f6516-d89f-7dcc-aa9a-37f1b99f53ff" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_SaleOfStockTerm_019f6516-d89f-7dea-a2be-e29992926984" xlink:href="xndu-20260630.xsd#xndu_SaleOfStockTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019f6516-af58-7a88-8d76-8e0de54273ec" xlink:to="loc_xndu_SaleOfStockTerm_019f6516-d89f-7dea-a2be-e29992926984" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_SaleOfStockMaximumAmountIssuable_019fc862-d8b2-7d36-9615-a791d168b4a7" xlink:href="xndu-20260630.xsd#xndu_SaleOfStockMaximumAmountIssuable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019f6516-af58-7a88-8d76-8e0de54273ec" xlink:to="loc_xndu_SaleOfStockMaximumAmountIssuable_019fc862-d8b2-7d36-9615-a791d168b4a7" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssets_019fa727-cd76-7029-b0c9-b79528d7d1a3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019f6516-af58-7a88-8d76-8e0de54273ec" xlink:to="loc_us-gaap_DerivativeAssets_019fa727-cd76-7029-b0c9-b79528d7d1a3" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLossOnDerivative_019fa727-cd76-70ba-b013-7bc0963655a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLossOnDerivative"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019f6516-af58-7a88-8d76-8e0de54273ec" xlink:to="loc_us-gaap_DerivativeLossOnDerivative_019fa727-cd76-70ba-b013-7bc0963655a0" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_DerivativeInstrumentContingentConsiderationLiabilityShares_019faab0-3b35-7e4a-a6fe-da2887fab0b2" xlink:href="xndu-20260630.xsd#xndu_DerivativeInstrumentContingentConsiderationLiabilityShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019f6516-af58-7a88-8d76-8e0de54273ec" xlink:to="loc_xndu_DerivativeInstrumentContingentConsiderationLiabilityShares_019faab0-3b35-7e4a-a6fe-da2887fab0b2" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_DerivativeLiabilityContingentConsiderationRemainingSharesAvailableForIssuance_019faab1-7dd6-7184-8110-c937c8bd9017" xlink:href="xndu-20260630.xsd#xndu_DerivativeLiabilityContingentConsiderationRemainingSharesAvailableForIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019f6516-af58-7a88-8d76-8e0de54273ec" xlink:to="loc_xndu_DerivativeLiabilityContingentConsiderationRemainingSharesAvailableForIssuance_019faab1-7dd6-7184-8110-c937c8bd9017" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightOutstanding_019fa727-cd76-714a-ad6b-90af6471ec6b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019f6516-af58-7a88-8d76-8e0de54273ec" xlink:to="loc_us-gaap_ClassOfWarrantOrRightOutstanding_019fa727-cd76-714a-ad6b-90af6471ec6b" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/ShareholdersEquityScheduleofStockIssuedandOutstandingDetails" xlink:type="simple" xlink:href="xndu-20260630.xsd#ShareholdersEquityScheduleofStockIssuedandOutstandingDetails"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/ShareholdersEquityScheduleofStockIssuedandOutstandingDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_019e92e9-54be-75a4-8b7e-a36c14970b5a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_019e92e9-54be-7e50-bf33-6d16b19c43dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_019e92e9-54be-75a4-8b7e-a36c14970b5a" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_019e92e9-54be-7e50-bf33-6d16b19c43dc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019e92e9-54be-7598-bec7-f76cb5617d49" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019e92e9-54be-7e50-bf33-6d16b19c43dc" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019e92e9-54be-7598-bec7-f76cb5617d49" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019e92e9-54be-7598-bec7-f76cb5617d49_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019e92e9-54be-7598-bec7-f76cb5617d49" xlink:to="loc_us-gaap_ClassOfStockDomain_019e92e9-54be-7598-bec7-f76cb5617d49_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019e92e9-54be-7a6f-b1a0-c2c05939171f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019e92e9-54be-7598-bec7-f76cb5617d49" xlink:to="loc_us-gaap_ClassOfStockDomain_019e92e9-54be-7a6f-b1a0-c2c05939171f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_XanaduClassAMultipleVotingSharesMember_019e92e9-54be-7a68-b856-8206d7654967" xlink:href="xndu-20260630.xsd#xndu_XanaduClassAMultipleVotingSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019e92e9-54be-7a6f-b1a0-c2c05939171f" xlink:to="loc_xndu_XanaduClassAMultipleVotingSharesMember_019e92e9-54be-7a68-b856-8206d7654967" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_XanaduClassBSubordinateVotingSharesEarnOutSharesMember_019e92e9-54be-7ce6-be41-7ce9b0b9010d" xlink:href="xndu-20260630.xsd#xndu_XanaduClassBSubordinateVotingSharesEarnOutSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019e92e9-54be-7a6f-b1a0-c2c05939171f" xlink:to="loc_xndu_XanaduClassBSubordinateVotingSharesEarnOutSharesMember_019e92e9-54be-7ce6-be41-7ce9b0b9010d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_OldXanaduConvertiblePreferredSharesMember_019e92e9-54be-7447-a5dd-c820cfd2fdf1" xlink:href="xndu-20260630.xsd#xndu_OldXanaduConvertiblePreferredSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019e92e9-54be-7a6f-b1a0-c2c05939171f" xlink:to="loc_xndu_OldXanaduConvertiblePreferredSharesMember_019e92e9-54be-7447-a5dd-c820cfd2fdf1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_OldXanaduCommonStockMember_019e92e9-54be-709c-ae01-37ae32967da7" xlink:href="xndu-20260630.xsd#xndu_OldXanaduCommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019e92e9-54be-7a6f-b1a0-c2c05939171f" xlink:to="loc_xndu_OldXanaduCommonStockMember_019e92e9-54be-709c-ae01-37ae32967da7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_019e92e9-54be-7788-92ab-28bd6d04e7e9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019e92e9-54be-75a4-8b7e-a36c14970b5a" xlink:to="loc_us-gaap_CommonStockSharesIssued_019e92e9-54be-7788-92ab-28bd6d04e7e9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019e92e9-54be-7214-bebc-eb66bb3a4111" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019e92e9-54be-75a4-8b7e-a36c14970b5a" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019e92e9-54be-7214-bebc-eb66bb3a4111" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_019e92e9-54be-74cc-9ad6-265aea038cad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019e92e9-54be-75a4-8b7e-a36c14970b5a" xlink:to="loc_us-gaap_CommonStockValue_019e92e9-54be-74cc-9ad6-265aea038cad" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValueOutstanding_019e92e9-54be-77ed-8b93-1db420c6a793" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockValueOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019e92e9-54be-75a4-8b7e-a36c14970b5a" xlink:to="loc_us-gaap_CommonStockValueOutstanding_019e92e9-54be-77ed-8b93-1db420c6a793" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesIssued_019e92e9-54be-75c0-858b-8597ecc732be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquitySharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019e92e9-54be-75a4-8b7e-a36c14970b5a" xlink:to="loc_us-gaap_TemporaryEquitySharesIssued_019e92e9-54be-75c0-858b-8597ecc732be" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesOutstanding_019e92e9-54be-73e1-b334-2c436160c572" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquitySharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019e92e9-54be-75a4-8b7e-a36c14970b5a" xlink:to="loc_us-gaap_TemporaryEquitySharesOutstanding_019e92e9-54be-73e1-b334-2c436160c572" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesIssued_019e92e9-54be-7806-9253-14914ada698b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019e92e9-54be-75a4-8b7e-a36c14970b5a" xlink:to="loc_us-gaap_SharesIssued_019e92e9-54be-7806-9253-14914ada698b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_019e92e9-54be-73f8-b939-2781eaf21c5a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019e92e9-54be-75a4-8b7e-a36c14970b5a" xlink:to="loc_us-gaap_SharesOutstanding_019e92e9-54be-73f8-b939-2781eaf21c5a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockValueOutstanding_019e92e9-54be-7947-9aa5-7bbc3080f1c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockValueOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019e92e9-54be-75a4-8b7e-a36c14970b5a" xlink:to="loc_us-gaap_PreferredStockValueOutstanding_019e92e9-54be-7947-9aa5-7bbc3080f1c5" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockValue_019e92e9-54be-7333-a392-90114ba41ae0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019e92e9-54be-75a4-8b7e-a36c14970b5a" xlink:to="loc_us-gaap_PreferredStockValue_019e92e9-54be-7333-a392-90114ba41ae0" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_SharesValueIssued_019e92e9-54be-737b-aa81-d8df388e7a51" xlink:href="xndu-20260630.xsd#xndu_SharesValueIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019e92e9-54be-75a4-8b7e-a36c14970b5a" xlink:to="loc_xndu_SharesValueIssued_019e92e9-54be-737b-aa81-d8df388e7a51" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_SharesValueOutstanding_019e92e9-54be-76e5-b20f-68ab17d5474c" xlink:href="xndu-20260630.xsd#xndu_SharesValueOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019e92e9-54be-75a4-8b7e-a36c14970b5a" xlink:to="loc_xndu_SharesValueOutstanding_019e92e9-54be-76e5-b20f-68ab17d5474c" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/ShareholdersEquityScheduleofChangesinSharesIssuedandOutstandingandShareCapitalDetails" xlink:type="simple" xlink:href="xndu-20260630.xsd#ShareholdersEquityScheduleofChangesinSharesIssuedandOutstandingandShareCapitalDetails"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/ShareholdersEquityScheduleofChangesinSharesIssuedandOutstandingandShareCapitalDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_019e92e9-54be-7d3c-bf0d-3161a16eef0f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_019e92e9-54be-72f1-b023-f728fcf21c22" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_019e92e9-54be-7d3c-bf0d-3161a16eef0f" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_019e92e9-54be-72f1-b023-f728fcf21c22" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019e92e9-54be-7d5f-9cd1-345d4b7c1ee1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019e92e9-54be-72f1-b023-f728fcf21c22" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019e92e9-54be-7d5f-9cd1-345d4b7c1ee1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019e92e9-54be-7d5f-9cd1-345d4b7c1ee1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019e92e9-54be-7d5f-9cd1-345d4b7c1ee1" xlink:to="loc_us-gaap_ClassOfStockDomain_019e92e9-54be-7d5f-9cd1-345d4b7c1ee1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019e92e9-54be-73bb-8e9b-edbcbb38f875" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019e92e9-54be-7d5f-9cd1-345d4b7c1ee1" xlink:to="loc_us-gaap_ClassOfStockDomain_019e92e9-54be-73bb-8e9b-edbcbb38f875" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_OldXanaduConvertiblePreferredSharesMember_019e92e9-54be-75f1-b0f1-f8a2cfe77ed0" xlink:href="xndu-20260630.xsd#xndu_OldXanaduConvertiblePreferredSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019e92e9-54be-73bb-8e9b-edbcbb38f875" xlink:to="loc_xndu_OldXanaduConvertiblePreferredSharesMember_019e92e9-54be-75f1-b0f1-f8a2cfe77ed0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_OldXanaduCommonStockMember_019e92e9-54be-75c0-a681-ffefc200bcd7" xlink:href="xndu-20260630.xsd#xndu_OldXanaduCommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019e92e9-54be-73bb-8e9b-edbcbb38f875" xlink:to="loc_xndu_OldXanaduCommonStockMember_019e92e9-54be-75c0-a681-ffefc200bcd7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_XanaduClassAMultipleVotingSharesMember_019e92e9-54be-7415-b4c4-659486998f13" xlink:href="xndu-20260630.xsd#xndu_XanaduClassAMultipleVotingSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019e92e9-54be-73bb-8e9b-edbcbb38f875" xlink:to="loc_xndu_XanaduClassAMultipleVotingSharesMember_019e92e9-54be-7415-b4c4-659486998f13" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_XanaduClassBSubordinateVotingSharesEarnOutSharesMember_019e92e9-54be-76fc-a685-cbf9be7ec80e" xlink:href="xndu-20260630.xsd#xndu_XanaduClassBSubordinateVotingSharesEarnOutSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019e92e9-54be-73bb-8e9b-edbcbb38f875" xlink:to="loc_xndu_XanaduClassBSubordinateVotingSharesEarnOutSharesMember_019e92e9-54be-76fc-a685-cbf9be7ec80e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019e92e9-54be-7f1a-b363-1977a8384b1c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019e92e9-54be-72f1-b023-f728fcf21c22" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019e92e9-54be-7f1a-b363-1977a8384b1c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019e92e9-54be-7f1a-b363-1977a8384b1c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019e92e9-54be-7f1a-b363-1977a8384b1c" xlink:to="loc_us-gaap_EquityComponentDomain_019e92e9-54be-7f1a-b363-1977a8384b1c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019e92e9-54be-798d-b66f-858ceec78e12" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019e92e9-54be-7f1a-b363-1977a8384b1c" xlink:to="loc_us-gaap_EquityComponentDomain_019e92e9-54be-798d-b66f-858ceec78e12" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019e92e9-54be-7663-895f-d92a0cb7ed27" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019e92e9-54be-798d-b66f-858ceec78e12" xlink:to="loc_us-gaap_CommonStockMember_019e92e9-54be-7663-895f-d92a0cb7ed27" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_019faac1-0573-7c8e-a90e-ba95f2f4b6b9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConversionOfStockByUniqueDescriptionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019e92e9-54be-72f1-b023-f728fcf21c22" xlink:to="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_019faac1-0573-7c8e-a90e-ba95f2f4b6b9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockNameDomain_019faac1-0573-7c8e-a90e-ba95f2f4b6b9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConversionOfStockNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_019faac1-0573-7c8e-a90e-ba95f2f4b6b9" xlink:to="loc_us-gaap_ConversionOfStockNameDomain_019faac1-0573-7c8e-a90e-ba95f2f4b6b9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockNameDomain_019faac1-0573-79cf-a004-c6d9049b7c58" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConversionOfStockNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_019faac1-0573-7c8e-a90e-ba95f2f4b6b9" xlink:to="loc_us-gaap_ConversionOfStockNameDomain_019faac1-0573-79cf-a004-c6d9049b7c58" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ConversionOfConvertiblePreferredStockMember_019faac1-62ff-7195-89d3-177916d0416b" xlink:href="xndu-20260630.xsd#xndu_ConversionOfConvertiblePreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockNameDomain_019faac1-0573-79cf-a004-c6d9049b7c58" xlink:to="loc_xndu_ConversionOfConvertiblePreferredStockMember_019faac1-62ff-7195-89d3-177916d0416b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ConversionOfEarnOutSharesMember_019faac1-9d86-78a5-b5c3-966a69cf1d36" xlink:href="xndu-20260630.xsd#xndu_ConversionOfEarnOutSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockNameDomain_019faac1-0573-79cf-a004-c6d9049b7c58" xlink:to="loc_xndu_ConversionOfEarnOutSharesMember_019faac1-9d86-78a5-b5c3-966a69cf1d36" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_019faabc-902b-7f2c-a2cb-776c3eaeaab6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInTemporaryEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019e92e9-54be-7d3c-bf0d-3161a16eef0f" xlink:to="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_019faabc-902b-7f2c-a2cb-776c3eaeaab6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesOutstanding_019e92e9-54be-7a77-a294-c6fa1ae7eb24" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquitySharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_019faabc-902b-7f2c-a2cb-776c3eaeaab6" xlink:to="loc_us-gaap_TemporaryEquitySharesOutstanding_019e92e9-54be-7a77-a294-c6fa1ae7eb24" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_019faabd-0572-7351-84fb-db132ef08bb7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityCarryingAmountAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_019faabc-902b-7f2c-a2cb-776c3eaeaab6" xlink:to="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_019faabd-0572-7351-84fb-db132ef08bb7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_TemporaryEquitySharesConversionOfConvertibleSecurities_019faabe-270c-79b6-a9c8-a37044b56025" xlink:href="xndu-20260630.xsd#xndu_TemporaryEquitySharesConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_019faabc-902b-7f2c-a2cb-776c3eaeaab6" xlink:to="loc_xndu_TemporaryEquitySharesConversionOfConvertibleSecurities_019faabe-270c-79b6-a9c8-a37044b56025" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_TemporaryEquityValueConversionOfConvertibleSecurities_019faabe-85d9-7116-a8e4-615437760f05" xlink:href="xndu-20260630.xsd#xndu_TemporaryEquityValueConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_019faabc-902b-7f2c-a2cb-776c3eaeaab6" xlink:to="loc_xndu_TemporaryEquityValueConversionOfConvertibleSecurities_019faabe-85d9-7116-a8e4-615437760f05" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesOutstanding_019e92e9-54be-76ab-a53f-584ac6d99171" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquitySharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_019faac0-4677-7a55-8c8e-395917287eb5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityCarryingAmountAttributableToParent"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-54be-71e1-83e1-de0a438cd656" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019e92e9-54be-7d3c-bf0d-3161a16eef0f" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-54be-71e1-83e1-de0a438cd656" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019e92e9-54be-7398-b87a-2850180c48e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-54be-71e1-83e1-de0a438cd656" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019e92e9-54be-7398-b87a-2850180c48e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019e92e9-54be-75fd-915c-e8a02cba4682" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-54be-71e1-83e1-de0a438cd656" xlink:to="loc_us-gaap_StockholdersEquity_019e92e9-54be-75fd-915c-e8a02cba4682" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019e92e9-54be-7053-bbf8-551fc65c1f2c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-54be-71e1-83e1-de0a438cd656" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019e92e9-54be-7053-bbf8-551fc65c1f2c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_019e92e9-54be-7bb4-87c6-aca468d4f2bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-54be-71e1-83e1-de0a438cd656" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_019e92e9-54be-7bb4-87c6-aca468d4f2bf" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_019e92e9-54be-7252-91e7-f1464e2c8195" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-54be-71e1-83e1-de0a438cd656" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_019e92e9-54be-7252-91e7-f1464e2c8195" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities_019e92e9-54be-7411-ae36-1b43b5881449" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-54be-71e1-83e1-de0a438cd656" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities_019e92e9-54be-7411-ae36-1b43b5881449" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_StockIssuedDuringPeriodSharesReverseRecapitalization_019e92e9-54be-7452-959b-5d897258389f" xlink:href="xndu-20260630.xsd#xndu_StockIssuedDuringPeriodSharesReverseRecapitalization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-54be-71e1-83e1-de0a438cd656" xlink:to="loc_xndu_StockIssuedDuringPeriodSharesReverseRecapitalization_019e92e9-54be-7452-959b-5d897258389f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_StockIssuedDuringPeriodValueReverseRecapitalization_019e92e9-54be-790f-b4e6-4f930ac5e11a" xlink:href="xndu-20260630.xsd#xndu_StockIssuedDuringPeriodValueReverseRecapitalization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-54be-71e1-83e1-de0a438cd656" xlink:to="loc_xndu_StockIssuedDuringPeriodValueReverseRecapitalization_019e92e9-54be-790f-b4e6-4f930ac5e11a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_StockReclassifiedDuringPeriodDerivativeLiabilityContingentConsiderationValue_019e92e9-54be-784a-9458-2425e306a887" xlink:href="xndu-20260630.xsd#xndu_StockReclassifiedDuringPeriodDerivativeLiabilityContingentConsiderationValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-54be-71e1-83e1-de0a438cd656" xlink:to="loc_xndu_StockReclassifiedDuringPeriodDerivativeLiabilityContingentConsiderationValue_019e92e9-54be-784a-9458-2425e306a887" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfUnits_019f8a0e-d597-78e1-b78b-c98b9f067938" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueConversionOfUnits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-54be-71e1-83e1-de0a438cd656" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfUnits_019f8a0e-d597-78e1-b78b-c98b9f067938" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019f8a11-6737-7682-aa0b-7795a19f775f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-54be-71e1-83e1-de0a438cd656" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019f8a11-6737-7682-aa0b-7795a19f775f" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_019f8a11-8631-7cfb-a2a0-f471b303270a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-54be-71e1-83e1-de0a438cd656" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_019f8a11-8631-7cfb-a2a0-f471b303270a" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesIssuedForServices_019f8a12-4621-78d0-bb24-6bea39692d6c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesIssuedForServices"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-54be-71e1-83e1-de0a438cd656" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesIssuedForServices_019f8a12-4621-78d0-bb24-6bea39692d6c" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueIssuedForServices_019f8a12-89b9-79ba-af7e-db565f9d5a91" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueIssuedForServices"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-54be-71e1-83e1-de0a438cd656" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueIssuedForServices_019f8a12-89b9-79ba-af7e-db565f9d5a91" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_StockIssuedDuringPeriodSharesExerciseOfWarrants_019e92e9-54be-74e0-9d8a-bdbc698583e5" xlink:href="xndu-20260630.xsd#xndu_StockIssuedDuringPeriodSharesExerciseOfWarrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-54be-71e1-83e1-de0a438cd656" xlink:to="loc_xndu_StockIssuedDuringPeriodSharesExerciseOfWarrants_019e92e9-54be-74e0-9d8a-bdbc698583e5" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_StockIssuedDuringPeriodValueExerciseOfWarrants_019e92e9-54be-7281-83e1-eaa5f9a55712" xlink:href="xndu-20260630.xsd#xndu_StockIssuedDuringPeriodValueExerciseOfWarrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e92e9-54be-71e1-83e1-de0a438cd656" xlink:to="loc_xndu_StockIssuedDuringPeriodValueExerciseOfWarrants_019e92e9-54be-7281-83e1-eaa5f9a55712" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019e92e9-54be-752c-84d9-628081ae5906" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019e92e9-54be-7541-a0da-002412e84a3f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/StockbasedCompensationNarrativeDetails" xlink:type="simple" xlink:href="xndu-20260630.xsd#StockbasedCompensationNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/StockbasedCompensationNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e92e9-54be-753e-bd28-69cb5989cca7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e92e9-54be-75c9-b193-fb77dd0f6c36" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e92e9-54be-753e-bd28-69cb5989cca7" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e92e9-54be-75c9-b193-fb77dd0f6c36" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_019e92e9-54be-794b-9530-5cb6599ee153" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e92e9-54be-75c9-b193-fb77dd0f6c36" xlink:to="loc_us-gaap_PlanNameAxis_019e92e9-54be-794b-9530-5cb6599ee153" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019e92e9-54be-794b-9530-5cb6599ee153_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_019e92e9-54be-794b-9530-5cb6599ee153" xlink:to="loc_us-gaap_PlanNameDomain_019e92e9-54be-794b-9530-5cb6599ee153_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019e92e9-54be-7ad2-be52-a32f0305053e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_019e92e9-54be-794b-9530-5cb6599ee153" xlink:to="loc_us-gaap_PlanNameDomain_019e92e9-54be-7ad2-be52-a32f0305053e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_A2017EquityIncentivePlanMember_019e92e9-54be-74c9-a48f-328816e0841a" xlink:href="xndu-20260630.xsd#xndu_A2017EquityIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019e92e9-54be-7ad2-be52-a32f0305053e" xlink:to="loc_xndu_A2017EquityIncentivePlanMember_019e92e9-54be-74c9-a48f-328816e0841a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_A2018EquityIncentivePlanMember_019e92e9-54be-7f9a-9c59-bb96855c6109" xlink:href="xndu-20260630.xsd#xndu_A2018EquityIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019e92e9-54be-7ad2-be52-a32f0305053e" xlink:to="loc_xndu_A2018EquityIncentivePlanMember_019e92e9-54be-7f9a-9c59-bb96855c6109" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_XanaduOmnibusLongTermIncentivePlanMember_019e92e9-54be-7d81-bd17-bb7f95b5b459" xlink:href="xndu-20260630.xsd#xndu_XanaduOmnibusLongTermIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019e92e9-54be-7ad2-be52-a32f0305053e" xlink:to="loc_xndu_XanaduOmnibusLongTermIncentivePlanMember_019e92e9-54be-7d81-bd17-bb7f95b5b459" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019e92e9-54be-7f75-87cf-94606290e57f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e92e9-54be-75c9-b193-fb77dd0f6c36" xlink:to="loc_us-gaap_AwardTypeAxis_019e92e9-54be-7f75-87cf-94606290e57f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e92e9-54be-7f75-87cf-94606290e57f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019e92e9-54be-7f75-87cf-94606290e57f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e92e9-54be-7f75-87cf-94606290e57f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e92e9-54be-7bf3-a684-7e37b36c6d75" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019e92e9-54be-7f75-87cf-94606290e57f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e92e9-54be-7bf3-a684-7e37b36c6d75" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019e92e9-54be-7488-9613-dd5071b42894" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e92e9-54be-7bf3-a684-7e37b36c6d75" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019e92e9-54be-7488-9613-dd5071b42894" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019fb7be-6f0d-728f-9fee-f567e0972d60" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e92e9-54be-7bf3-a684-7e37b36c6d75" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019fb7be-6f0d-728f-9fee-f567e0972d60" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingAxis_019e92e9-54be-7dad-a427-05e355626df7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e92e9-54be-75c9-b193-fb77dd0f6c36" xlink:to="loc_us-gaap_VestingAxis_019e92e9-54be-7dad-a427-05e355626df7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_019e92e9-54be-7dad-a427-05e355626df7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VestingAxis_019e92e9-54be-7dad-a427-05e355626df7" xlink:to="loc_us-gaap_VestingDomain_019e92e9-54be-7dad-a427-05e355626df7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_019e92e9-54be-78f9-9b86-d8b423c815ad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VestingAxis_019e92e9-54be-7dad-a427-05e355626df7" xlink:to="loc_us-gaap_VestingDomain_019e92e9-54be-78f9-9b86-d8b423c815ad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_019e92e9-54be-7cc1-8949-776d0d643752" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationAwardTrancheOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_019e92e9-54be-78f9-9b86-d8b423c815ad" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_019e92e9-54be-7cc1-8949-776d0d643752" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_019e92e9-54be-7969-8e8c-251ddb4746ae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationAwardTrancheTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_019e92e9-54be-78f9-9b86-d8b423c815ad" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_019e92e9-54be-7969-8e8c-251ddb4746ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_019e92e9-54be-7213-bf36-6b334f95b494" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e92e9-54be-753e-bd28-69cb5989cca7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_019e92e9-54be-7213-bf36-6b334f95b494" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_019e92e9-54be-7ae8-94b9-c02bd2edd55c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e92e9-54be-753e-bd28-69cb5989cca7" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_019e92e9-54be-7ae8-94b9-c02bd2edd55c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019e92e9-54be-75fa-9f01-9de87098f31f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e92e9-54be-753e-bd28-69cb5989cca7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019e92e9-54be-75fa-9f01-9de87098f31f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_019e92e9-54be-7860-8379-7db757bbdda0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e92e9-54be-753e-bd28-69cb5989cca7" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_019e92e9-54be-7860-8379-7db757bbdda0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ShareBasedCompensationArrangementByShareBasedPaymentAwardExpirationPeriodFromEmployeeTermination_019e92e9-54be-7556-9a29-8811cbebfe46" xlink:href="xndu-20260630.xsd#xndu_ShareBasedCompensationArrangementByShareBasedPaymentAwardExpirationPeriodFromEmployeeTermination"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e92e9-54be-753e-bd28-69cb5989cca7" xlink:to="loc_xndu_ShareBasedCompensationArrangementByShareBasedPaymentAwardExpirationPeriodFromEmployeeTermination_019e92e9-54be-7556-9a29-8811cbebfe46" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentageOfOutstandingStockMaximum_019e92e9-54be-7e15-b66e-df3cad6d8019" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentageOfOutstandingStockMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e92e9-54be-753e-bd28-69cb5989cca7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentageOfOutstandingStockMaximum_019e92e9-54be-7e15-b66e-df3cad6d8019" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_019e92e9-54be-79be-bf03-f169b1911299" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e92e9-54be-753e-bd28-69cb5989cca7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_019e92e9-54be-79be-bf03-f169b1911299" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_019e92e9-54be-70c7-8b0b-7ac67aa34acf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e92e9-54be-753e-bd28-69cb5989cca7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_019e92e9-54be-70c7-8b0b-7ac67aa34acf" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount_019e92e9-54be-7de5-be81-66475ab9fb5d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e92e9-54be-753e-bd28-69cb5989cca7" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount_019e92e9-54be-7de5-be81-66475ab9fb5d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_019e92e9-54be-7637-a814-6c24c862603b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e92e9-54be-753e-bd28-69cb5989cca7" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_019e92e9-54be-7637-a814-6c24c862603b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019e92e9-54be-7648-b74d-05fb51ac1314" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e92e9-54be-753e-bd28-69cb5989cca7" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019e92e9-54be-7648-b74d-05fb51ac1314" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/StockbasedCompensationScheduleofStockOptionActivityDetails" xlink:type="simple" xlink:href="xndu-20260630.xsd#StockbasedCompensationScheduleofStockOptionActivityDetails"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/StockbasedCompensationScheduleofStockOptionActivityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e92e9-54be-7fa0-bfc8-0bb7dd688499" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e92e9-54be-7fe3-8792-c95143613b44" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e92e9-54be-7fa0-bfc8-0bb7dd688499" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e92e9-54be-7fe3-8792-c95143613b44" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019e92e9-54be-7855-bfa4-d72f2e38927e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e92e9-54be-7fe3-8792-c95143613b44" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019e92e9-54be-7855-bfa4-d72f2e38927e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019e92e9-54be-7855-bfa4-d72f2e38927e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019e92e9-54be-7855-bfa4-d72f2e38927e" xlink:to="loc_us-gaap_ClassOfStockDomain_019e92e9-54be-7855-bfa4-d72f2e38927e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019e92e9-54be-715e-b8d6-648b1c519569" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019e92e9-54be-7855-bfa4-d72f2e38927e" xlink:to="loc_us-gaap_ClassOfStockDomain_019e92e9-54be-715e-b8d6-648b1c519569" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_XanaduClassAMultipleVotingSharesMember_019e92e9-54be-7aa5-9c48-9ca531a6be02" xlink:href="xndu-20260630.xsd#xndu_XanaduClassAMultipleVotingSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019e92e9-54be-715e-b8d6-648b1c519569" xlink:to="loc_xndu_XanaduClassAMultipleVotingSharesMember_019e92e9-54be-7aa5-9c48-9ca531a6be02" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_XanaduClassBSubordinateVotingSharesEarnOutSharesMember_019e92e9-54be-7686-95cc-d9cf064a024f" xlink:href="xndu-20260630.xsd#xndu_XanaduClassBSubordinateVotingSharesEarnOutSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019e92e9-54be-715e-b8d6-648b1c519569" xlink:to="loc_xndu_XanaduClassBSubordinateVotingSharesEarnOutSharesMember_019e92e9-54be-7686-95cc-d9cf064a024f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_019e92e9-54be-716f-932a-1c2caf806d2b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e92e9-54be-7fa0-bfc8-0bb7dd688499" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_019e92e9-54be-716f-932a-1c2caf806d2b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_019e92e9-54be-7af8-ad5f-8ad502f94d2a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_019e92e9-54be-716f-932a-1c2caf806d2b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_019e92e9-54be-7af8-ad5f-8ad502f94d2a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_019e92e9-54be-7941-87b1-ba0d13555a1d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_019e92e9-54be-716f-932a-1c2caf806d2b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_019e92e9-54be-7941-87b1-ba0d13555a1d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019e92e9-54be-7fab-8de7-b1dad9f4377c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_019e92e9-54be-716f-932a-1c2caf806d2b" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019e92e9-54be-7fab-8de7-b1dad9f4377c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod_019e92e9-54be-7873-85c3-393134e3bbbf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_019e92e9-54be-716f-932a-1c2caf806d2b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod_019e92e9-54be-7873-85c3-393134e3bbbf" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_019e92e9-54be-76e9-9be0-fe944572c542" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_019e92e9-54be-739b-9589-70b255680796" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e92e9-54be-7fa0-bfc8-0bb7dd688499" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_019e92e9-54be-739b-9589-70b255680796" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_019e92e9-54be-7435-96eb-ce908c3c83ce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_019e92e9-54be-739b-9589-70b255680796" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_019e92e9-54be-7435-96eb-ce908c3c83ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_019e92e9-54be-71bf-87db-cc4f711fb361" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_019e92e9-54be-739b-9589-70b255680796" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_019e92e9-54be-71bf-87db-cc4f711fb361" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_019e92e9-54be-7132-89a1-fb5aced9b20f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_019e92e9-54be-739b-9589-70b255680796" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_019e92e9-54be-7132-89a1-fb5aced9b20f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriodWeightedAverageExercisePrice_019e92e9-54be-77e2-9495-b070bd400af6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_019e92e9-54be-739b-9589-70b255680796" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriodWeightedAverageExercisePrice_019e92e9-54be-77e2-9495-b070bd400af6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_019e92e9-54be-78cd-bc19-8df17c655887" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_019e92e9-54be-77a2-b8e8-d29284d33f14" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e92e9-54be-7fa0-bfc8-0bb7dd688499" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_019e92e9-54be-77a2-b8e8-d29284d33f14" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_019e92e9-54be-79df-a569-e0fbac0540a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_019e92e9-54be-77a2-b8e8-d29284d33f14" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_019e92e9-54be-79df-a569-e0fbac0540a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_019e92e9-54be-7ec3-993e-85ba2a339b29" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_019e92e9-54be-77a2-b8e8-d29284d33f14" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_019e92e9-54be-7ec3-993e-85ba2a339b29" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_019e92e9-54be-745d-a885-41ab379a71fd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_019e92e9-54be-77a2-b8e8-d29284d33f14" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_019e92e9-54be-745d-a885-41ab379a71fd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_019e92e9-54be-7e60-9de2-080f0bda8063" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_019e92e9-54be-77a2-b8e8-d29284d33f14" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_019e92e9-54be-7e60-9de2-080f0bda8063" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_019e92e9-54be-7521-8532-481847fd0ccd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_019e92e9-54be-77a2-b8e8-d29284d33f14" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_019e92e9-54be-7521-8532-481847fd0ccd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_019e92e9-54be-7bde-9ad8-a5ad0748981d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_019e92e9-54be-77a2-b8e8-d29284d33f14" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_019e92e9-54be-7bde-9ad8-a5ad0748981d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfShares_019e92e9-54be-7f87-9501-33fcc82bd5e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_019e92e9-54be-77a2-b8e8-d29284d33f14" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfShares_019e92e9-54be-7f87-9501-33fcc82bd5e8" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedWeightedAverageGrantDateFairValue_019e92e9-54be-7092-a36c-7a65e5a9bac9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_019e92e9-54be-77a2-b8e8-d29284d33f14" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedWeightedAverageGrantDateFairValue_019e92e9-54be-7092-a36c-7a65e5a9bac9" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsNonvestedWeightedAverageRemainingContractualTerm_019e92e9-54be-7d30-9e8a-4140c7653089" xlink:href="xndu-20260630.xsd#xndu_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsNonvestedWeightedAverageRemainingContractualTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_019e92e9-54be-77a2-b8e8-d29284d33f14" xlink:to="loc_xndu_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsNonvestedWeightedAverageRemainingContractualTerm_019e92e9-54be-7d30-9e8a-4140c7653089" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsNonvestedIntrinsicValue_019e92e9-54be-7c5f-a484-1cd55d2f5bf3" xlink:href="xndu-20260630.xsd#xndu_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsNonvestedIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_019e92e9-54be-77a2-b8e8-d29284d33f14" xlink:to="loc_xndu_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsNonvestedIntrinsicValue_019e92e9-54be-7c5f-a484-1cd55d2f5bf3" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/StockbasedCompensationScheduleofRestrictedStockUnitsDetails" xlink:type="simple" xlink:href="xndu-20260630.xsd#StockbasedCompensationScheduleofRestrictedStockUnitsDetails"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/StockbasedCompensationScheduleofRestrictedStockUnitsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019f25a6-e5aa-7123-a683-57c78bbe4b78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019f25a6-e5aa-73b4-952f-ed122c340d52" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019f25a6-e5aa-7123-a683-57c78bbe4b78" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019f25a6-e5aa-73b4-952f-ed122c340d52" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019f25a6-e5aa-7cb3-aa10-a47a59bfc483" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019f25a6-e5aa-73b4-952f-ed122c340d52" xlink:to="loc_us-gaap_AwardTypeAxis_019f25a6-e5aa-7cb3-aa10-a47a59bfc483" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019f25a6-e5aa-7cb3-aa10-a47a59bfc483_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019f25a6-e5aa-7cb3-aa10-a47a59bfc483" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019f25a6-e5aa-7cb3-aa10-a47a59bfc483_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019f25a6-e5aa-7a03-9770-88730d0c16ac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019f25a6-e5aa-7cb3-aa10-a47a59bfc483" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019f25a6-e5aa-7a03-9770-88730d0c16ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019f25a6-e5aa-729c-b864-c515e98af196" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019f25a6-e5aa-7a03-9770-88730d0c16ac" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019f25a6-e5aa-729c-b864-c515e98af196" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_019f25a7-6f02-7c45-a5ae-3bce991ac647" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019f25a6-e5aa-7123-a683-57c78bbe4b78" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_019f25a7-6f02-7c45-a5ae-3bce991ac647" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019f25a6-e5aa-70e8-a8ca-166332839ce8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_019f25a7-6f02-7c45-a5ae-3bce991ac647" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019f25a6-e5aa-70e8-a8ca-166332839ce8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019f25a7-ee0b-7d54-b2d1-f9006e63f6e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_019f25a7-6f02-7c45-a5ae-3bce991ac647" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019f25a7-ee0b-7d54-b2d1-f9006e63f6e8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_019f25a7-ee0b-7912-bdcc-94507325ccc6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_019f25a7-6f02-7c45-a5ae-3bce991ac647" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_019f25a7-ee0b-7912-bdcc-94507325ccc6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019f25a9-ad7d-72e0-adf9-93b8355211c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019f25a7-ee0b-70fd-a53b-c5f8e1d4aec9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019f25a6-e5aa-7123-a683-57c78bbe4b78" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019f25a7-ee0b-70fd-a53b-c5f8e1d4aec9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsUnvestedNumber_019f25a7-ee0b-7b10-8a50-813e83cfad6a" xlink:href="xndu-20260630.xsd#xndu_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsUnvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019f25a6-e5aa-7123-a683-57c78bbe4b78" xlink:to="loc_xndu_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsUnvestedNumber_019f25a7-ee0b-7b10-8a50-813e83cfad6a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019f25aa-6bb5-73f2-b3ca-1c316f1ca305" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019f25a6-e5aa-7123-a683-57c78bbe4b78" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019f25aa-6bb5-73f2-b3ca-1c316f1ca305" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019f25aa-9a1e-73e0-9ad6-486bf316c505" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019f25aa-6bb5-73f2-b3ca-1c316f1ca305" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019f25aa-9a1e-73e0-9ad6-486bf316c505" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019f25aa-9a1e-72b7-9562-a1aed3c0e972" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019f25aa-6bb5-73f2-b3ca-1c316f1ca305" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019f25aa-9a1e-72b7-9562-a1aed3c0e972" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresIntrinsicValue_019f25aa-9a1e-7c4a-84a3-710ffdf9c581" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019f25aa-6bb5-73f2-b3ca-1c316f1ca305" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresIntrinsicValue_019f25aa-9a1e-7c4a-84a3-710ffdf9c581" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019f25ac-3536-797a-9617-73971efa72e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_019f25aa-9a1e-7606-9a1f-1d899d50eaa8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019f25aa-6bb5-73f2-b3ca-1c316f1ca305" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_019f25aa-9a1e-7606-9a1f-1d899d50eaa8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsUnvestedWeightedAverageGrantDateFairValue_019f25aa-9a1e-7fbe-820f-7b3f5792dca8" xlink:href="xndu-20260630.xsd#xndu_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsUnvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019f25aa-6bb5-73f2-b3ca-1c316f1ca305" xlink:to="loc_xndu_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsUnvestedWeightedAverageGrantDateFairValue_019f25aa-9a1e-7fbe-820f-7b3f5792dca8" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/StockbasedCompensationScheduleofStockbasedCompensationExpenseDetails" xlink:type="simple" xlink:href="xndu-20260630.xsd#StockbasedCompensationScheduleofStockbasedCompensationExpenseDetails"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/StockbasedCompensationScheduleofStockbasedCompensationExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e92e9-54be-76cb-b0e8-91939d66295b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019e92e9-54be-73d9-a773-ac486e9b1117" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e92e9-54be-76cb-b0e8-91939d66295b" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019e92e9-54be-73d9-a773-ac486e9b1117" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019e92e9-54be-724e-8041-c001e4eb7be7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019e92e9-54be-73d9-a773-ac486e9b1117" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019e92e9-54be-724e-8041-c001e4eb7be7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardCompensationCost1_019e92e9-54be-772f-9333-61c83165cfb7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardCompensationCost1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e92e9-54be-76cb-b0e8-91939d66295b" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardCompensationCost1_019e92e9-54be-772f-9333-61c83165cfb7" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/StockbasedCompensationScheduleofStockbasedCompensationExpenseDetails_1" xlink:type="simple" xlink:href="xndu-20260630.xsd#StockbasedCompensationScheduleofStockbasedCompensationExpenseDetails_1"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/StockbasedCompensationScheduleofStockbasedCompensationExpenseDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e92e9-54be-76cb-b0e8-91939d66295b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019e92e9-54be-73d9-a773-ac486e9b1117" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e92e9-54be-76cb-b0e8-91939d66295b" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019e92e9-54be-73d9-a773-ac486e9b1117" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardCompensationCost1_019e92e9-54be-772f-9333-61c83165cfb7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardCompensationCost1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e92e9-54be-76cb-b0e8-91939d66295b" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardCompensationCost1_019e92e9-54be-772f-9333-61c83165cfb7" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/NetLossPerShareScheduleofAntidilutiveSecuritiesExcludedfromComputationofNetLossPerShareDetails" xlink:type="simple" xlink:href="xndu-20260630.xsd#NetLossPerShareScheduleofAntidilutiveSecuritiesExcludedfromComputationofNetLossPerShareDetails"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/NetLossPerShareScheduleofAntidilutiveSecuritiesExcludedfromComputationofNetLossPerShareDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019e92e9-54be-74f2-9196-03d68c632e5d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019e92e9-54be-77a3-87b1-8ede10c609a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019e92e9-54be-74f2-9196-03d68c632e5d" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019e92e9-54be-77a3-87b1-8ede10c609a0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019e92e9-54be-7919-8a11-bc353eed6b86" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019e92e9-54be-77a3-87b1-8ede10c609a0" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019e92e9-54be-7919-8a11-bc353eed6b86" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e92e9-54be-7919-8a11-bc353eed6b86_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019e92e9-54be-7919-8a11-bc353eed6b86" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e92e9-54be-7919-8a11-bc353eed6b86_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e92e9-54be-79b8-b48e-135692938e38" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019e92e9-54be-7919-8a11-bc353eed6b86" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e92e9-54be-79b8-b48e-135692938e38" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_019e92e9-54be-7f65-a148-67c01e154e12" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e92e9-54be-79b8-b48e-135692938e38" xlink:to="loc_us-gaap_WarrantMember_019e92e9-54be-7f65-a148-67c01e154e12" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019e92e9-54be-71ed-ad86-dc636ea58e37" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e92e9-54be-79b8-b48e-135692938e38" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019e92e9-54be-71ed-ad86-dc636ea58e37" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertiblePreferredStockMember_019e92e9-54be-7e31-8a6b-f138bd2295dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertiblePreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e92e9-54be-79b8-b48e-135692938e38" xlink:to="loc_us-gaap_ConvertiblePreferredStockMember_019e92e9-54be-7e31-8a6b-f138bd2295dc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019e92e9-54be-705a-9311-ba2a71950195" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019e92e9-54be-74f2-9196-03d68c632e5d" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019e92e9-54be-705a-9311-ba2a71950195" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/SegmentInformationScheduleofSegmentInformationDetails" xlink:type="simple" xlink:href="xndu-20260630.xsd#SegmentInformationScheduleofSegmentInformationDetails"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/SegmentInformationScheduleofSegmentInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019e92e9-54be-7618-beb7-bbae9574ea21" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e92e9-54be-7820-8783-cb59e055aab1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e92e9-54be-7618-beb7-bbae9574ea21" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e92e9-54be-7820-8783-cb59e055aab1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019e92e9-54be-77df-b22e-ad91b66f37ab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e92e9-54be-7820-8783-cb59e055aab1" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019e92e9-54be-77df-b22e-ad91b66f37ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019e92e9-54be-77df-b22e-ad91b66f37ab_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019e92e9-54be-77df-b22e-ad91b66f37ab" xlink:to="loc_us-gaap_SegmentDomain_019e92e9-54be-77df-b22e-ad91b66f37ab_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019e92e9-54be-7f06-bfee-9a2304d8c81a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019e92e9-54be-77df-b22e-ad91b66f37ab" xlink:to="loc_us-gaap_SegmentDomain_019e92e9-54be-7f06-bfee-9a2304d8c81a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ReportableSegmentMember_019e92e9-54be-75fa-9ab7-dd1ee65e3269" xlink:href="xndu-20260630.xsd#xndu_ReportableSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019e92e9-54be-7f06-bfee-9a2304d8c81a" xlink:to="loc_xndu_ReportableSegmentMember_019e92e9-54be-75fa-9ab7-dd1ee65e3269" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e92e9-54be-7268-adb7-35f3ae8b5892" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e92e9-54be-7618-beb7-bbae9574ea21" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e92e9-54be-7268-adb7-35f3ae8b5892" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfRevenue_019e92e9-54be-7689-bafe-edd12a549290" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e92e9-54be-7618-beb7-bbae9574ea21" xlink:to="loc_us-gaap_CostOfRevenue_019e92e9-54be-7689-bafe-edd12a549290" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_019e92e9-54be-7052-92a3-2c1a5aebdb41" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e92e9-54be-7618-beb7-bbae9574ea21" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_019e92e9-54be-7052-92a3-2c1a5aebdb41" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_019e92e9-54be-71e0-8ed6-f8abf1d0d5ba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e92e9-54be-7618-beb7-bbae9574ea21" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_019e92e9-54be-71e0-8ed6-f8abf1d0d5ba" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingAndMarketingExpense_019e92e9-54be-724c-a050-e326aa17cd56" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SellingAndMarketingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e92e9-54be-7618-beb7-bbae9574ea21" xlink:to="loc_us-gaap_SellingAndMarketingExpense_019e92e9-54be-724c-a050-e326aa17cd56" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LaborAndRelatedExpense_019e92e9-54be-7bde-8a36-cb7b355a51df" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LaborAndRelatedExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e92e9-54be-7618-beb7-bbae9574ea21" xlink:to="loc_us-gaap_LaborAndRelatedExpense_019e92e9-54be-7bde-8a36-cb7b355a51df" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_019e92e9-54be-71d6-8c3e-8626d1793a88" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e92e9-54be-7618-beb7-bbae9574ea21" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_019e92e9-54be-71d6-8c3e-8626d1793a88" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeExpenseNet_019e92e9-54be-727a-afbb-c96554853472" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestIncomeExpenseNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e92e9-54be-7618-beb7-bbae9574ea21" xlink:to="loc_us-gaap_InterestIncomeExpenseNet_019e92e9-54be-727a-afbb-c96554853472" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingOtherItemAmount_019e92e9-54be-73ee-8093-eb9518bfabd1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingOtherItemAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e92e9-54be-7618-beb7-bbae9574ea21" xlink:to="loc_us-gaap_SegmentReportingOtherItemAmount_019e92e9-54be-73ee-8093-eb9518bfabd1" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019e92e9-54be-775e-9fc8-b5c5a0271782" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e92e9-54be-7618-beb7-bbae9574ea21" xlink:to="loc_us-gaap_NetIncomeLoss_019e92e9-54be-775e-9fc8-b5c5a0271782" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.xanadu.ai/role/SubsequentEventsDetails" xlink:type="simple" xlink:href="xndu-20260630.xsd#SubsequentEventsDetails"/>
  <link:definitionLink xlink:role="http://www.xanadu.ai/role/SubsequentEventsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventLineItems_019e92e9-54be-7ed9-bb79-4104055a84ba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTable_019e92e9-54be-738c-acec-bfe36cfb4f83" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_019e92e9-54be-7ed9-bb79-4104055a84ba" xlink:to="loc_us-gaap_SubsequentEventTable_019e92e9-54be-738c-acec-bfe36cfb4f83" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_019e92e9-54be-7fc7-91f6-0cd8d708e9ca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019e92e9-54be-738c-acec-bfe36cfb4f83" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_019e92e9-54be-7fc7-91f6-0cd8d708e9ca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019e92e9-54be-7fc7-91f6-0cd8d708e9ca_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019e92e9-54be-7fc7-91f6-0cd8d708e9ca" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019e92e9-54be-7fc7-91f6-0cd8d708e9ca_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019e92e9-54be-70c7-b759-b1e7bb60cb98" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019e92e9-54be-7fc7-91f6-0cd8d708e9ca" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019e92e9-54be-70c7-b759-b1e7bb60cb98" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_019e92e9-54be-7cc6-858d-5d41d8370829" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_019e92e9-54be-70c7-b759-b1e7bb60cb98" xlink:to="loc_us-gaap_SubsequentEventMember_019e92e9-54be-7cc6-858d-5d41d8370829" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_019fb1e5-6b41-7a46-b5ea-e67876b0cb03" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019e92e9-54be-738c-acec-bfe36cfb4f83" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_019fb1e5-6b41-7a46-b5ea-e67876b0cb03" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019fb1e5-6b41-7a46-b5ea-e67876b0cb03_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019fb1e5-6b41-7a46-b5ea-e67876b0cb03" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019fb1e5-6b41-7a46-b5ea-e67876b0cb03_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019fb1e5-6b41-7b0c-9876-2e77187ecdd9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019fb1e5-6b41-7a46-b5ea-e67876b0cb03" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019fb1e5-6b41-7b0c-9876-2e77187ecdd9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_SVSWarrantsMember_019fb1e5-6b41-7545-9750-cb78842faf6f" xlink:href="xndu-20260630.xsd#xndu_SVSWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019fb1e5-6b41-7b0c-9876-2e77187ecdd9" xlink:to="loc_xndu_SVSWarrantsMember_019fb1e5-6b41-7545-9750-cb78842faf6f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightOutstanding_019fb1e5-6b41-71cc-9eaf-2bced18c0210" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019e92e9-54be-7ed9-bb79-4104055a84ba" xlink:to="loc_us-gaap_ClassOfWarrantOrRightOutstanding_019fb1e5-6b41-71cc-9eaf-2bced18c0210" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_xndu_ClassOfWarrantOrRightNumberOfWarrantsSurrenderedToCoverExercisePrice_019fc685-b49e-7e52-a39b-771cc544dd6a" xlink:href="xndu-20260630.xsd#xndu_ClassOfWarrantOrRightNumberOfWarrantsSurrenderedToCoverExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019e92e9-54be-7ed9-bb79-4104055a84ba" xlink:to="loc_xndu_ClassOfWarrantOrRightNumberOfWarrantsSurrenderedToCoverExercisePrice_019fc685-b49e-7e52-a39b-771cc544dd6a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019fb1e5-6b41-711c-85c1-530db5893026" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019e92e9-54be-7ed9-bb79-4104055a84ba" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019fb1e5-6b41-711c-85c1-530db5893026" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019fc685-b49e-754b-b327-a0597379948a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019e92e9-54be-7ed9-bb79-4104055a84ba" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019fc685-b49e-754b-b327-a0597379948a" xlink:type="arc" order="3"/>
  </link:definitionLink>
</link:linkbase>
