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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019e8332-cc5f-704f-9fcb-ba0bd484aae3,g:7528a1a7-2399-4796-b23c-af8f234ed657-->
<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://ouster.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONSANDCOMPREHENSIVELOSS" xlink:type="simple" xlink:href="oust-20260630.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONSANDCOMPREHENSIVELOSS"/>
  <link:definitionLink xlink:role="http://ouster.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONSANDCOMPREHENSIVELOSS" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019e8332-cd1b-718e-8828-cf82126a44ec" 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_019e8332-cd1b-7232-b3ad-15e59796659e" 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_019e8332-cd1b-718e-8828-cf82126a44ec" xlink:to="loc_us-gaap_StatementTable_019e8332-cd1b-7232-b3ad-15e59796659e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019e8332-cd1b-7fb9-8075-aa76e579838b" 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_StatementTable_019e8332-cd1b-7232-b3ad-15e59796659e" xlink:to="loc_srt_ProductOrServiceAxis_019e8332-cd1b-7fb9-8075-aa76e579838b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019e8332-cd1b-7fb9-8075-aa76e579838b_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_019e8332-cd1b-7fb9-8075-aa76e579838b" xlink:to="loc_srt_ProductsAndServicesDomain_019e8332-cd1b-7fb9-8075-aa76e579838b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019e8332-cd1b-70ac-a69e-04a997fd9d05" 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_019e8332-cd1b-7fb9-8075-aa76e579838b" xlink:to="loc_srt_ProductsAndServicesDomain_019e8332-cd1b-70ac-a69e-04a997fd9d05" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductMember_019e8332-cd1b-7751-9253-ddd0afc6f921" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProductMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019e8332-cd1b-70ac-a69e-04a997fd9d05" xlink:to="loc_us-gaap_ProductMember_019e8332-cd1b-7751-9253-ddd0afc6f921" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RoyaltyMember_019e8332-cd1b-781d-9cae-c7cbea2c2d0a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RoyaltyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019e8332-cd1b-70ac-a69e-04a997fd9d05" xlink:to="loc_us-gaap_RoyaltyMember_019e8332-cd1b-781d-9cae-c7cbea2c2d0a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e8332-cd1b-7da1-a48c-86a96c407dcc" 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_StatementLineItems_019e8332-cd1b-718e-8828-cf82126a44ec" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e8332-cd1b-7da1-a48c-86a96c407dcc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfRevenue_019e8332-cd1b-7f73-a98e-967a574be3e8" 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_StatementLineItems_019e8332-cd1b-718e-8828-cf82126a44ec" xlink:to="loc_us-gaap_CostOfRevenue_019e8332-cd1b-7f73-a98e-967a574be3e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrossProfit_019e8332-cd1b-76c5-8e13-ee5c263e114e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GrossProfit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e8332-cd1b-718e-8828-cf82126a44ec" xlink:to="loc_us-gaap_GrossProfit_019e8332-cd1b-76c5-8e13-ee5c263e114e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpensesAbstract_019e8332-cd1b-7729-959d-8011fe4f7dc3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e8332-cd1b-718e-8828-cf82126a44ec" xlink:to="loc_us-gaap_OperatingExpensesAbstract_019e8332-cd1b-7729-959d-8011fe4f7dc3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_019e8332-cd1b-7927-842b-4d211eaef06c" 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_OperatingExpensesAbstract_019e8332-cd1b-7729-959d-8011fe4f7dc3" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_019e8332-cd1b-7927-842b-4d211eaef06c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingAndMarketingExpense_019e8332-cd1b-7104-ae35-89991d74ccc6" 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_OperatingExpensesAbstract_019e8332-cd1b-7729-959d-8011fe4f7dc3" xlink:to="loc_us-gaap_SellingAndMarketingExpense_019e8332-cd1b-7104-ae35-89991d74ccc6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_019e8332-cd1b-733f-8289-8ecc21e1c0b0" 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_OperatingExpensesAbstract_019e8332-cd1b-7729-959d-8011fe4f7dc3" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_019e8332-cd1b-733f-8289-8ecc21e1c0b0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpenses_019e8332-cd1b-79e5-880c-50068f5fe05d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019e8332-cd1b-7729-959d-8011fe4f7dc3" xlink:to="loc_us-gaap_OperatingExpenses_019e8332-cd1b-79e5-880c-50068f5fe05d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_019e8332-cd1b-7bca-8a04-a1da2dd14e07" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e8332-cd1b-718e-8828-cf82126a44ec" xlink:to="loc_us-gaap_OperatingIncomeLoss_019e8332-cd1b-7bca-8a04-a1da2dd14e07" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019e8332-cd1b-7340-bf99-bf4dbbab028e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonoperatingIncomeExpenseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e8332-cd1b-718e-8828-cf82126a44ec" xlink:to="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019e8332-cd1b-7340-bf99-bf4dbbab028e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeInterest_019e8332-cd1b-72fa-878c-fb3da3f6a592" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentIncomeInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019e8332-cd1b-7340-bf99-bf4dbbab028e" xlink:to="loc_us-gaap_InvestmentIncomeInterest_019e8332-cd1b-72fa-878c-fb3da3f6a592" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_019e8332-cd1b-74c1-88e1-79ab969b68d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019e8332-cd1b-7340-bf99-bf4dbbab028e" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_019e8332-cd1b-74c1-88e1-79ab969b68d8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_019e8332-cd1b-7037-8305-130708e32170" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e8332-cd1b-718e-8828-cf82126a44ec" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_019e8332-cd1b-7037-8305-130708e32170" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019e8332-cd1b-7f39-ba49-741d9d5c71b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e8332-cd1b-718e-8828-cf82126a44ec" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019e8332-cd1b-7f39-ba49-741d9d5c71b3" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_019e8332-cd1b-7f83-bef9-3744dc3fcd0d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e8332-cd1b-718e-8828-cf82126a44ec" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_019e8332-cd1b-7f83-bef9-3744dc3fcd0d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019e8332-cd1b-7845-b11b-824032b20044" 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_StatementLineItems_019e8332-cd1b-718e-8828-cf82126a44ec" xlink:to="loc_us-gaap_NetIncomeLoss_019e8332-cd1b-7845-b11b-824032b20044" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_019e8332-cd1b-72d1-b24f-1843beedb00b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e8332-cd1b-718e-8828-cf82126a44ec" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_019e8332-cd1b-72d1-b24f-1843beedb00b" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax_019e8332-cd1b-7ce5-b511-0fd87df0dc40" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_019e8332-cd1b-72d1-b24f-1843beedb00b" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax_019e8332-cd1b-7ce5-b511-0fd87df0dc40" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_019e8332-cd1b-78dc-9106-44af173ad280" 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_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_019e8332-cd1b-72d1-b24f-1843beedb00b" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_019e8332-cd1b-78dc-9106-44af173ad280" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTax_019e8332-cd1b-7169-9def-802104185365" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ComprehensiveIncomeNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_019e8332-cd1b-72d1-b24f-1843beedb00b" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTax_019e8332-cd1b-7169-9def-802104185365" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_019e8332-cd1b-7460-ba72-a7b8becda1c0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e8332-cd1b-718e-8828-cf82126a44ec" xlink:to="loc_us-gaap_EarningsPerShareBasic_019e8332-cd1b-7460-ba72-a7b8becda1c0" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_019e8332-cd1b-71a9-9bf9-d1135b3423cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e8332-cd1b-718e-8828-cf82126a44ec" xlink:to="loc_us-gaap_EarningsPerShareDiluted_019e8332-cd1b-71a9-9bf9-d1135b3423cb" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_019e8332-cd1b-701a-bd99-21545f822ae4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e8332-cd1b-718e-8828-cf82126a44ec" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_019e8332-cd1b-701a-bd99-21545f822ae4" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_019e8332-cd1b-7a0f-866f-96709aa15108" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e8332-cd1b-718e-8828-cf82126a44ec" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_019e8332-cd1b-7a0f-866f-96709aa15108" xlink:type="arc" order="14"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY" xlink:type="simple" xlink:href="oust-20260630.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY"/>
  <link:definitionLink xlink:role="http://ouster.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019e8332-cd1b-7221-8806-29fc3a24cf66" 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_019e8332-cd1b-71d2-a5d8-3cedba1ea059" 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_019e8332-cd1b-7221-8806-29fc3a24cf66" xlink:to="loc_us-gaap_StatementTable_019e8332-cd1b-71d2-a5d8-3cedba1ea059" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019e8332-cd1b-7779-8125-6f347c1c21c6" 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_019e8332-cd1b-71d2-a5d8-3cedba1ea059" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019e8332-cd1b-7779-8125-6f347c1c21c6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019e8332-cd1b-7779-8125-6f347c1c21c6_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_019e8332-cd1b-7779-8125-6f347c1c21c6" xlink:to="loc_us-gaap_EquityComponentDomain_019e8332-cd1b-7779-8125-6f347c1c21c6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019e8332-cd1b-7404-993a-9d465c5e3d99" 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_019e8332-cd1b-7779-8125-6f347c1c21c6" xlink:to="loc_us-gaap_EquityComponentDomain_019e8332-cd1b-7404-993a-9d465c5e3d99" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019e8332-cd1b-7ba4-8ce7-77dcba61ac85" 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_019e8332-cd1b-7404-993a-9d465c5e3d99" xlink:to="loc_us-gaap_CommonStockMember_019e8332-cd1b-7ba4-8ce7-77dcba61ac85" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019e8332-cd1b-7084-bc86-a64a6a1917ba" 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_019e8332-cd1b-7404-993a-9d465c5e3d99" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019e8332-cd1b-7084-bc86-a64a6a1917ba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019e8332-cd1b-7c3b-8583-cff270c72cbb" 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_019e8332-cd1b-7404-993a-9d465c5e3d99" xlink:to="loc_us-gaap_RetainedEarningsMember_019e8332-cd1b-7c3b-8583-cff270c72cbb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019e8332-cd1b-7127-a910-fee4eed01691" 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_019e8332-cd1b-7404-993a-9d465c5e3d99" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019e8332-cd1b-7127-a910-fee4eed01691" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cd1b-7c6b-a90d-e83c4c90c1dd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019e8332-cd1b-71d2-a5d8-3cedba1ea059" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cd1b-7c6b-a90d-e83c4c90c1dd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cd1b-7c6b-a90d-e83c4c90c1dd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cd1b-7c6b-a90d-e83c4c90c1dd" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cd1b-7c6b-a90d-e83c4c90c1dd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cd1b-77b9-9b4e-68b25ddaa92c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cd1b-7c6b-a90d-e83c4c90c1dd" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cd1b-77b9-9b4e-68b25ddaa92c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_StereoLabsMember_019e8332-cd1b-71b5-bfd0-df18ecf12242" xlink:href="oust-20260630.xsd#oust_StereoLabsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cd1b-77b9-9b4e-68b25ddaa92c" xlink:to="loc_oust_StereoLabsMember_019e8332-cd1b-71b5-bfd0-df18ecf12242" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_VelodyneMergerMember_019e8332-cd1b-72ad-82c5-10c6543871ea" xlink:href="oust-20260630.xsd#oust_VelodyneMergerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cd1b-77b9-9b4e-68b25ddaa92c" xlink:to="loc_oust_VelodyneMergerMember_019e8332-cd1b-72ad-82c5-10c6543871ea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e8332-cd1b-7f49-9055-a404e9567a87" 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_019e8332-cd1b-7221-8806-29fc3a24cf66" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e8332-cd1b-7f49-9055-a404e9567a87" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019e8332-cd1b-78cf-b857-db51459e3401" 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_019e8332-cd1b-7f49-9055-a404e9567a87" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019e8332-cd1b-78cf-b857-db51459e3401" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019e8332-cd1b-7cbb-88da-ad3511c51e04" 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_019e8332-cd1b-7f49-9055-a404e9567a87" xlink:to="loc_us-gaap_StockholdersEquity_019e8332-cd1b-7cbb-88da-ad3511c51e04" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019e8332-cd1b-709b-8a72-d7bc3366da81" 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_019e8332-cd1b-7f49-9055-a404e9567a87" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019e8332-cd1b-709b-8a72-d7bc3366da81" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_019e8332-cd1b-7ea5-b462-74367dc1dfc9" 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_019e8332-cd1b-7f49-9055-a404e9567a87" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_019e8332-cd1b-7ea5-b462-74367dc1dfc9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019f2165-99cf-7d8e-81d5-254bc16c75a3" 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_019e8332-cd1b-7f49-9055-a404e9567a87" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019f2165-99cf-7d8e-81d5-254bc16c75a3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_019f2165-99cf-79c3-b718-749112d96260" 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_019e8332-cd1b-7f49-9055-a404e9567a87" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_019f2165-99cf-79c3-b718-749112d96260" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesAcquisitions_019e8332-cd1b-7569-b97e-abd9b40a17e3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesAcquisitions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e8332-cd1b-7f49-9055-a404e9567a87" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesAcquisitions_019e8332-cd1b-7569-b97e-abd9b40a17e3" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueAcquisitions_019e8332-cd1b-7a06-9736-a74f7a3f3d28" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueAcquisitions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e8332-cd1b-7f49-9055-a404e9567a87" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueAcquisitions_019e8332-cd1b-7a06-9736-a74f7a3f3d28" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockSharesIssuedNetOfSharesForTaxWithholdings_019e8332-cd1b-71f7-bcf8-139296f7989e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockSharesIssuedNetOfSharesForTaxWithholdings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e8332-cd1b-7f49-9055-a404e9567a87" xlink:to="loc_us-gaap_RestrictedStockSharesIssuedNetOfSharesForTaxWithholdings_019e8332-cd1b-71f7-bcf8-139296f7989e" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardForfeited_019e8332-cd1b-71d9-b226-c3dea4da2b9a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardForfeited"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e8332-cd1b-7f49-9055-a404e9567a87" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardForfeited_019e8332-cd1b-71d9-b226-c3dea4da2b9a" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_019f2166-e3fe-73c1-9d17-2d3d90065034" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e8332-cd1b-7f49-9055-a404e9567a87" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_019f2166-e3fe-73c1-9d17-2d3d90065034" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_019f2166-e3fe-76f9-af93-a877bc189279" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e8332-cd1b-7f49-9055-a404e9567a87" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_019f2166-e3fe-76f9-af93-a877bc189279" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockAndWarrantsIssuedDuringPeriodValuePreferredStockAndWarrants_019e8332-cd1b-7760-add7-c646aa78e458" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockAndWarrantsIssuedDuringPeriodValuePreferredStockAndWarrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e8332-cd1b-7f49-9055-a404e9567a87" xlink:to="loc_us-gaap_StockAndWarrantsIssuedDuringPeriodValuePreferredStockAndWarrants_019e8332-cd1b-7760-add7-c646aa78e458" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019e8332-cd1b-7d5d-9df0-4cc5b0472271" 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_019e8332-cd1b-7f49-9055-a404e9567a87" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019e8332-cd1b-7d5d-9df0-4cc5b0472271" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019e8332-cd1b-7c3f-b678-964bb34715b4" 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_019e8332-cd1b-7f49-9055-a404e9567a87" xlink:to="loc_us-gaap_NetIncomeLoss_019e8332-cd1b-7c3f-b678-964bb34715b4" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_019e8332-cd1b-72ff-8d98-c096f2b36d65" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e8332-cd1b-7f49-9055-a404e9567a87" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_019e8332-cd1b-72ff-8d98-c096f2b36d65" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019e8332-cd1b-744b-b7c9-2523bc12ca81" 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_019e8332-cd1b-7be2-b305-4e7c168547e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/SummaryofSignificantAccountingPoliciesNarrativeDetails" xlink:type="simple" xlink:href="oust-20260630.xsd#SummaryofSignificantAccountingPoliciesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://ouster.com/role/SummaryofSignificantAccountingPoliciesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_019f21b7-48f5-7516-a26f-319f498402e6" 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_019f21b7-48f5-76b1-a220-5e07def31f3b" 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_019f21b7-48f5-7516-a26f-319f498402e6" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_019f21b7-48f5-76b1-a220-5e07def31f3b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainContingenciesByNatureAxis_019f8a74-fb18-7849-9b21-18bad9c2f05a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainContingenciesByNatureAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019f21b7-48f5-76b1-a220-5e07def31f3b" xlink:to="loc_us-gaap_GainContingenciesByNatureAxis_019f8a74-fb18-7849-9b21-18bad9c2f05a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainContingencyNatureDomain_019f8a74-fb18-7849-9b21-18bad9c2f05a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_GainContingenciesByNatureAxis_019f8a74-fb18-7849-9b21-18bad9c2f05a" xlink:to="loc_us-gaap_GainContingencyNatureDomain_019f8a74-fb18-7849-9b21-18bad9c2f05a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainContingencyNatureDomain_019f8a74-fb18-7806-b2c5-5ed40f5e5900" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_GainContingenciesByNatureAxis_019f8a74-fb18-7849-9b21-18bad9c2f05a" xlink:to="loc_us-gaap_GainContingencyNatureDomain_019f8a74-fb18-7806-b2c5-5ed40f5e5900" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_IEEPATariffRefundMember_019f8a74-fb18-793b-9286-e77a00e37273" xlink:href="oust-20260630.xsd#oust_IEEPATariffRefundMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GainContingencyNatureDomain_019f8a74-fb18-7806-b2c5-5ed40f5e5900" xlink:to="loc_oust_IEEPATariffRefundMember_019f8a74-fb18-793b-9286-e77a00e37273" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019f21b7-48f5-7b3f-a655-2f6253d80c7a" 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_DisaggregationOfRevenueTable_019f21b7-48f5-76b1-a220-5e07def31f3b" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019f21b7-48f5-7b3f-a655-2f6253d80c7a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_019faf5b-f0cc-7cf9-a191-ed40ba652911" 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_DisaggregationOfRevenueTable_019f21b7-48f5-76b1-a220-5e07def31f3b" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_019faf5b-f0cc-7cf9-a191-ed40ba652911" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019faf5b-f0cc-7cf9-a191-ed40ba652911_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_019faf5b-f0cc-7cf9-a191-ed40ba652911" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019faf5b-f0cc-7cf9-a191-ed40ba652911_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019faf5b-f0cc-767d-beda-a710426ec4fb" 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_019faf5b-f0cc-7cf9-a191-ed40ba652911" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019faf5b-f0cc-767d-beda-a710426ec4fb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_019faf5c-10dd-71ae-95a1-88555674b694" 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_019faf5b-f0cc-767d-beda-a710426ec4fb" xlink:to="loc_us-gaap_SubsequentEventMember_019faf5c-10dd-71ae-95a1-88555674b694" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_IEEPATariffRefundClaimsSubmitted_019fb2f3-98c2-7d81-a5b9-8be4b3a07cb1" xlink:href="oust-20260630.xsd#oust_IEEPATariffRefundClaimsSubmitted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019f21b7-48f5-7516-a26f-319f498402e6" xlink:to="loc_oust_IEEPATariffRefundClaimsSubmitted_019fb2f3-98c2-7d81-a5b9-8be4b3a07cb1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RecoveryOfDirectCosts_019f8a74-fb18-7d8e-8b80-2ad20f5968d0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RecoveryOfDirectCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019f21b7-48f5-7516-a26f-319f498402e6" xlink:to="loc_us-gaap_RecoveryOfDirectCosts_019f8a74-fb18-7d8e-8b80-2ad20f5968d0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivableForRecoveryOfImportDutiesNet_019f8a74-fb18-7fae-97d2-1941713d3113" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReceivableForRecoveryOfImportDutiesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019f21b7-48f5-7516-a26f-319f498402e6" xlink:to="loc_us-gaap_ReceivableForRecoveryOfImportDutiesNet_019f8a74-fb18-7fae-97d2-1941713d3113" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_CARESActEmployeeRetentionCredit_019f21b7-48f5-7a9e-a611-bb9708788d0f" xlink:href="oust-20260630.xsd#oust_CARESActEmployeeRetentionCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019f21b7-48f5-7516-a26f-319f498402e6" xlink:to="loc_oust_CARESActEmployeeRetentionCredit_019f21b7-48f5-7a9e-a611-bb9708788d0f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_CashCashEquivalentsAndRestrictedCashFDICInsuredAmount_019e8332-cddb-7f42-89f2-74b2cbcbe596" xlink:href="oust-20260630.xsd#oust_CashCashEquivalentsAndRestrictedCashFDICInsuredAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019f21b7-48f5-7516-a26f-319f498402e6" xlink:to="loc_oust_CashCashEquivalentsAndRestrictedCashFDICInsuredAmount_019e8332-cddb-7f42-89f2-74b2cbcbe596" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_CashCashEquivalentsAndRestrictedCashUninsuredAmount_019e8332-cddb-7386-8a6b-e900a895290c" xlink:href="oust-20260630.xsd#oust_CashCashEquivalentsAndRestrictedCashUninsuredAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019f21b7-48f5-7516-a26f-319f498402e6" xlink:to="loc_oust_CashCashEquivalentsAndRestrictedCashUninsuredAmount_019e8332-cddb-7386-8a6b-e900a895290c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ThresholdPeriodPastDueForWriteoffOfTradeAccountsReceivable_019e8332-cddb-7e5a-bb1c-e88f835b3d38" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ThresholdPeriodPastDueForWriteoffOfTradeAccountsReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019f21b7-48f5-7516-a26f-319f498402e6" xlink:to="loc_us-gaap_ThresholdPeriodPastDueForWriteoffOfTradeAccountsReceivable_019e8332-cddb-7e5a-bb1c-e88f835b3d38" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/SummaryofSignificantAccountingPoliciesNarrativeDetails_1" xlink:type="simple" xlink:href="oust-20260630.xsd#SummaryofSignificantAccountingPoliciesNarrativeDetails_1"/>
  <link:definitionLink xlink:role="http://ouster.com/role/SummaryofSignificantAccountingPoliciesNarrativeDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_019f21b7-48f5-7516-a26f-319f498402e6" 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_019f21b7-48f5-76b1-a220-5e07def31f3b" 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_019f21b7-48f5-7516-a26f-319f498402e6" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_019f21b7-48f5-76b1-a220-5e07def31f3b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainContingenciesByNatureAxis_019f8a74-fb18-7849-9b21-18bad9c2f05a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainContingenciesByNatureAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019f21b7-48f5-76b1-a220-5e07def31f3b" xlink:to="loc_us-gaap_GainContingenciesByNatureAxis_019f8a74-fb18-7849-9b21-18bad9c2f05a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainContingencyNatureDomain_019f8a74-fb18-7849-9b21-18bad9c2f05a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_GainContingenciesByNatureAxis_019f8a74-fb18-7849-9b21-18bad9c2f05a" xlink:to="loc_us-gaap_GainContingencyNatureDomain_019f8a74-fb18-7849-9b21-18bad9c2f05a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainContingencyNatureDomain_019f8a74-fb18-7806-b2c5-5ed40f5e5900" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_GainContingenciesByNatureAxis_019f8a74-fb18-7849-9b21-18bad9c2f05a" xlink:to="loc_us-gaap_GainContingencyNatureDomain_019f8a74-fb18-7806-b2c5-5ed40f5e5900" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_IEEPATariffRefundMember_019f8a74-fb18-793b-9286-e77a00e37273" xlink:href="oust-20260630.xsd#oust_IEEPATariffRefundMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GainContingencyNatureDomain_019f8a74-fb18-7806-b2c5-5ed40f5e5900" xlink:to="loc_oust_IEEPATariffRefundMember_019f8a74-fb18-793b-9286-e77a00e37273" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_019faf5b-f0cc-7cf9-a191-ed40ba652911" 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_DisaggregationOfRevenueTable_019f21b7-48f5-76b1-a220-5e07def31f3b" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_019faf5b-f0cc-7cf9-a191-ed40ba652911" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019faf5b-f0cc-7cf9-a191-ed40ba652911_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_019faf5b-f0cc-7cf9-a191-ed40ba652911" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019faf5b-f0cc-7cf9-a191-ed40ba652911_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019faf5b-f0cc-767d-beda-a710426ec4fb" 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_019faf5b-f0cc-7cf9-a191-ed40ba652911" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019faf5b-f0cc-767d-beda-a710426ec4fb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_019faf5c-10dd-71ae-95a1-88555674b694" 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_019faf5b-f0cc-767d-beda-a710426ec4fb" xlink:to="loc_us-gaap_SubsequentEventMember_019faf5c-10dd-71ae-95a1-88555674b694" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_IEEPATariffRefundClaimsSubmitted_019fb2f3-98c2-7d81-a5b9-8be4b3a07cb1" xlink:href="oust-20260630.xsd#oust_IEEPATariffRefundClaimsSubmitted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019f21b7-48f5-7516-a26f-319f498402e6" xlink:to="loc_oust_IEEPATariffRefundClaimsSubmitted_019fb2f3-98c2-7d81-a5b9-8be4b3a07cb1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RecoveryOfDirectCosts_019f8a74-fb18-7d8e-8b80-2ad20f5968d0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RecoveryOfDirectCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019f21b7-48f5-7516-a26f-319f498402e6" xlink:to="loc_us-gaap_RecoveryOfDirectCosts_019f8a74-fb18-7d8e-8b80-2ad20f5968d0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivableForRecoveryOfImportDutiesNet_019f8a74-fb18-7fae-97d2-1941713d3113" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReceivableForRecoveryOfImportDutiesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019f21b7-48f5-7516-a26f-319f498402e6" xlink:to="loc_us-gaap_ReceivableForRecoveryOfImportDutiesNet_019f8a74-fb18-7fae-97d2-1941713d3113" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_CARESActEmployeeRetentionCredit_019f21b7-48f5-7a9e-a611-bb9708788d0f" xlink:href="oust-20260630.xsd#oust_CARESActEmployeeRetentionCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019f21b7-48f5-7516-a26f-319f498402e6" xlink:to="loc_oust_CARESActEmployeeRetentionCredit_019f21b7-48f5-7a9e-a611-bb9708788d0f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_CashCashEquivalentsAndRestrictedCashFDICInsuredAmount_019e8332-cddb-7f42-89f2-74b2cbcbe596" xlink:href="oust-20260630.xsd#oust_CashCashEquivalentsAndRestrictedCashFDICInsuredAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019f21b7-48f5-7516-a26f-319f498402e6" xlink:to="loc_oust_CashCashEquivalentsAndRestrictedCashFDICInsuredAmount_019e8332-cddb-7f42-89f2-74b2cbcbe596" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_CashCashEquivalentsAndRestrictedCashUninsuredAmount_019e8332-cddb-7386-8a6b-e900a895290c" xlink:href="oust-20260630.xsd#oust_CashCashEquivalentsAndRestrictedCashUninsuredAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019f21b7-48f5-7516-a26f-319f498402e6" xlink:to="loc_oust_CashCashEquivalentsAndRestrictedCashUninsuredAmount_019e8332-cddb-7386-8a6b-e900a895290c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ThresholdPeriodPastDueForWriteoffOfTradeAccountsReceivable_019e8332-cddb-7e5a-bb1c-e88f835b3d38" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ThresholdPeriodPastDueForWriteoffOfTradeAccountsReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019f21b7-48f5-7516-a26f-319f498402e6" xlink:to="loc_us-gaap_ThresholdPeriodPastDueForWriteoffOfTradeAccountsReceivable_019e8332-cddb-7e5a-bb1c-e88f835b3d38" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/SummaryofSignificantAccountingPoliciesScheduleofConcentrationRiskDetails" xlink:type="simple" xlink:href="oust-20260630.xsd#SummaryofSignificantAccountingPoliciesScheduleofConcentrationRiskDetails"/>
  <link:definitionLink xlink:role="http://ouster.com/role/SummaryofSignificantAccountingPoliciesScheduleofConcentrationRiskDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskLineItems_019e8332-cddb-722c-b19f-194c789fc8e9" 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_019e8332-cddb-79ba-96f4-f4a65038ead3" 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_019e8332-cddb-722c-b19f-194c789fc8e9" xlink:to="loc_us-gaap_ConcentrationRiskTable_019e8332-cddb-79ba-96f4-f4a65038ead3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_019e8332-cddb-79e9-82e9-6a9019673373" 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_019e8332-cddb-79ba-96f4-f4a65038ead3" xlink:to="loc_srt_MajorCustomersAxis_019e8332-cddb-79e9-82e9-6a9019673373" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019e8332-cddb-79e9-82e9-6a9019673373_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_019e8332-cddb-79e9-82e9-6a9019673373" xlink:to="loc_srt_NameOfMajorCustomerDomain_019e8332-cddb-79e9-82e9-6a9019673373_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019e8332-cddb-74ec-ad44-a11e0d20cb59" 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_019e8332-cddb-79e9-82e9-6a9019673373" xlink:to="loc_srt_NameOfMajorCustomerDomain_019e8332-cddb-74ec-ad44-a11e0d20cb59" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_CustomerAMember_019e8332-cddb-750a-bfa9-98cf9e25e0f0" xlink:href="oust-20260630.xsd#oust_CustomerAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019e8332-cddb-74ec-ad44-a11e0d20cb59" xlink:to="loc_oust_CustomerAMember_019e8332-cddb-750a-bfa9-98cf9e25e0f0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_CustomerBMember_019e8332-cddb-7936-abe9-df4e1cfcd6a7" xlink:href="oust-20260630.xsd#oust_CustomerBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019e8332-cddb-74ec-ad44-a11e0d20cb59" xlink:to="loc_oust_CustomerBMember_019e8332-cddb-7936-abe9-df4e1cfcd6a7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_CustomerDMember_019e8332-cddb-7c1c-8df6-d1a3a65996a8" xlink:href="oust-20260630.xsd#oust_CustomerDMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019e8332-cddb-74ec-ad44-a11e0d20cb59" xlink:to="loc_oust_CustomerDMember_019e8332-cddb-7c1c-8df6-d1a3a65996a8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_CustomerEMember_019e8332-cddb-793f-9caa-6d61ae5b3dc6" xlink:href="oust-20260630.xsd#oust_CustomerEMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019e8332-cddb-74ec-ad44-a11e0d20cb59" xlink:to="loc_oust_CustomerEMember_019e8332-cddb-793f-9caa-6d61ae5b3dc6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_CustomerFMember_019e8332-cddb-74c6-a429-863369d4f274" xlink:href="oust-20260630.xsd#oust_CustomerFMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019e8332-cddb-74ec-ad44-a11e0d20cb59" xlink:to="loc_oust_CustomerFMember_019e8332-cddb-74c6-a429-863369d4f274" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_CustomerGMember_019f1d73-779d-7403-b4d0-847fe0197322" xlink:href="oust-20260630.xsd#oust_CustomerGMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019e8332-cddb-74ec-ad44-a11e0d20cb59" xlink:to="loc_oust_CustomerGMember_019f1d73-779d-7403-b4d0-847fe0197322" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019e8332-cddb-726b-81da-495b3eaedd3b" 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_019e8332-cddb-79ba-96f4-f4a65038ead3" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019e8332-cddb-726b-81da-495b3eaedd3b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e8332-cddb-726b-81da-495b3eaedd3b_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_019e8332-cddb-726b-81da-495b3eaedd3b" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e8332-cddb-726b-81da-495b3eaedd3b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e8332-cddb-732e-92e7-001755696a0b" 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_019e8332-cddb-726b-81da-495b3eaedd3b" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e8332-cddb-732e-92e7-001755696a0b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableMember_019e8332-cddb-7767-a1ee-8472c0be7060" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e8332-cddb-732e-92e7-001755696a0b" xlink:to="loc_us-gaap_AccountsReceivableMember_019e8332-cddb-7767-a1ee-8472c0be7060" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_019e8332-cddb-7972-9baa-be1cdd5de9a4" 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_019e8332-cddb-732e-92e7-001755696a0b" xlink:to="loc_us-gaap_SalesRevenueNetMember_019e8332-cddb-7972-9baa-be1cdd5de9a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsTotalMember_019e8332-cddb-7864-a4fc-bb1ffcd11172" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfGoodsTotalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e8332-cddb-732e-92e7-001755696a0b" xlink:to="loc_us-gaap_CostOfGoodsTotalMember_019e8332-cddb-7864-a4fc-bb1ffcd11172" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableMember_019e8332-cddb-7a95-b2b6-75ba6e0b5001" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsPayableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e8332-cddb-732e-92e7-001755696a0b" xlink:to="loc_us-gaap_AccountsPayableMember_019e8332-cddb-7a95-b2b6-75ba6e0b5001" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_019e8332-cddb-7a96-9727-8996e6e91a5e" 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_019e8332-cddb-79ba-96f4-f4a65038ead3" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_019e8332-cddb-7a96-9727-8996e6e91a5e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019e8332-cddb-7a96-9727-8996e6e91a5e_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_019e8332-cddb-7a96-9727-8996e6e91a5e" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019e8332-cddb-7a96-9727-8996e6e91a5e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019e8332-cddb-7f51-97ce-8926518017b4" 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_019e8332-cddb-7a96-9727-8996e6e91a5e" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019e8332-cddb-7f51-97ce-8926518017b4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_019e8332-cddb-7e6e-85a3-870ddf3dae8b" 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_019e8332-cddb-7f51-97ce-8926518017b4" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_019e8332-cddb-7e6e-85a3-870ddf3dae8b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplierConcentrationRiskMember_019e8332-cddb-79a0-bf82-bd5891ab48c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SupplierConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019e8332-cddb-7f51-97ce-8926518017b4" xlink:to="loc_us-gaap_SupplierConcentrationRiskMember_019e8332-cddb-79a0-bf82-bd5891ab48c5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionBySupplierAxis_019e8332-cddb-714d-b57c-b4fd14ac291b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionBySupplierAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_019e8332-cddb-79ba-96f4-f4a65038ead3" xlink:to="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionBySupplierAxis_019e8332-cddb-714d-b57c-b4fd14ac291b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_019e8332-cddb-714d-b57c-b4fd14ac291b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionBySupplierAxis_019e8332-cddb-714d-b57c-b4fd14ac291b" xlink:to="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_019e8332-cddb-714d-b57c-b4fd14ac291b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_019e8332-cddb-773e-a34f-62436171fc31" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionBySupplierAxis_019e8332-cddb-714d-b57c-b4fd14ac291b" xlink:to="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_019e8332-cddb-773e-a34f-62436171fc31" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_SupplierAMember_019e8332-cddb-7720-9915-cab8d2e80c6f" xlink:href="oust-20260630.xsd#oust_SupplierAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_019e8332-cddb-773e-a34f-62436171fc31" xlink:to="loc_oust_SupplierAMember_019e8332-cddb-7720-9915-cab8d2e80c6f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_SupplierBMember_019e8332-cddb-74dd-b78c-b12a49ae43a4" xlink:href="oust-20260630.xsd#oust_SupplierBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_019e8332-cddb-773e-a34f-62436171fc31" xlink:to="loc_oust_SupplierBMember_019e8332-cddb-74dd-b78c-b12a49ae43a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_SupplierCMember_019e8332-cddb-7259-8b81-70b331597ea2" xlink:href="oust-20260630.xsd#oust_SupplierCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_019e8332-cddb-773e-a34f-62436171fc31" xlink:to="loc_oust_SupplierCMember_019e8332-cddb-7259-8b81-70b331597ea2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_019e8332-cddb-7e59-b265-14a9c0b68bf8" 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_019e8332-cddb-722c-b19f-194c789fc8e9" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_019e8332-cddb-7e59-b265-14a9c0b68bf8" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/BusinessCombinationandRelatedTransactionsNarrativeDetails" xlink:type="simple" xlink:href="oust-20260630.xsd#BusinessCombinationandRelatedTransactionsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://ouster.com/role/BusinessCombinationandRelatedTransactionsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7c02-b12e-cd647bbfde78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019e8332-cddb-71f4-8804-a9df27eb3315" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7c02-b12e-cd647bbfde78" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019e8332-cddb-71f4-8804-a9df27eb3315" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddb-7b16-a7c7-4be05584915d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019e8332-cddb-71f4-8804-a9df27eb3315" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddb-7b16-a7c7-4be05584915d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddb-7b16-a7c7-4be05584915d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddb-7b16-a7c7-4be05584915d" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddb-7b16-a7c7-4be05584915d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddb-797e-98bc-8fdfd10453b7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddb-7b16-a7c7-4be05584915d" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddb-797e-98bc-8fdfd10453b7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_StereoLabsMember_019e8332-cddb-74ca-9de8-cde8c58eaccf" xlink:href="oust-20260630.xsd#oust_StereoLabsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddb-797e-98bc-8fdfd10453b7" xlink:to="loc_oust_StereoLabsMember_019e8332-cddb-74ca-9de8-cde8c58eaccf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityInterestIssuedOrIssuableByTypeAxis_019e8332-cddb-7da1-930c-d18ec85a26f4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityInterestIssuedOrIssuableByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019e8332-cddb-71f4-8804-a9df27eb3315" xlink:to="loc_us-gaap_EquityInterestIssuedOrIssuableByTypeAxis_019e8332-cddb-7da1-930c-d18ec85a26f4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityInterestIssuedOrIssuableTypeDomain_019e8332-cddb-7da1-930c-d18ec85a26f4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityInterestIssuedOrIssuableTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_EquityInterestIssuedOrIssuableByTypeAxis_019e8332-cddb-7da1-930c-d18ec85a26f4" xlink:to="loc_us-gaap_EquityInterestIssuedOrIssuableTypeDomain_019e8332-cddb-7da1-930c-d18ec85a26f4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityInterestIssuedOrIssuableTypeDomain_019e8332-cddb-7493-b9f8-0e69ccdaaf5b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityInterestIssuedOrIssuableTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_EquityInterestIssuedOrIssuableByTypeAxis_019e8332-cddb-7da1-930c-d18ec85a26f4" xlink:to="loc_us-gaap_EquityInterestIssuedOrIssuableTypeDomain_019e8332-cddb-7493-b9f8-0e69ccdaaf5b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019e8332-cddb-7a0d-9fe5-3fbdc732f4fc" 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_EquityInterestIssuedOrIssuableTypeDomain_019e8332-cddb-7493-b9f8-0e69ccdaaf5b" xlink:to="loc_us-gaap_CommonStockMember_019e8332-cddb-7a0d-9fe5-3fbdc732f4fc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_019e8332-cddb-7cd5-b4a6-ab97ee908426" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7c02-b12e-cd647bbfde78" xlink:to="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_019e8332-cddb-7cd5-b4a6-ab97ee908426" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_019e8332-cddb-7a8b-85cd-880707c1606d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7c02-b12e-cd647bbfde78" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_019e8332-cddb-7a8b-85cd-880707c1606d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesAcquisitions_019e8332-cddb-7b12-929c-317b38dbb7cd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesAcquisitions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7c02-b12e-cd647bbfde78" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesAcquisitions_019e8332-cddb-7b12-929c-317b38dbb7cd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_019f3eff-a754-72e8-85c5-2990951fee62" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7c02-b12e-cd647bbfde78" xlink:to="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_019f3eff-a754-72e8-85c5-2990951fee62" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_BusinessCombinationConsiderationTransferredEquityInterestIssuedAndIssuableSharesSubjectToLockUpArrangement_019e8332-cddb-7444-8add-4cab793dcc59" xlink:href="oust-20260630.xsd#oust_BusinessCombinationConsiderationTransferredEquityInterestIssuedAndIssuableSharesSubjectToLockUpArrangement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7c02-b12e-cd647bbfde78" xlink:to="loc_oust_BusinessCombinationConsiderationTransferredEquityInterestIssuedAndIssuableSharesSubjectToLockUpArrangement_019e8332-cddb-7444-8add-4cab793dcc59" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_BusinessCombinationStaggeredLockUpArrangementForSharesServicePeriod_019e8332-cddb-7315-a10a-a47d8e7481b9" xlink:href="oust-20260630.xsd#oust_BusinessCombinationStaggeredLockUpArrangementForSharesServicePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7c02-b12e-cd647bbfde78" xlink:to="loc_oust_BusinessCombinationStaggeredLockUpArrangementForSharesServicePeriod_019e8332-cddb-7315-a10a-a47d8e7481b9" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_BusinessCombinationStaggeredLockUpArrangementSharesVestingPercent_019e8332-cddb-7b33-a500-f8e377371b7e" xlink:href="oust-20260630.xsd#oust_BusinessCombinationStaggeredLockUpArrangementSharesVestingPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7c02-b12e-cd647bbfde78" xlink:to="loc_oust_BusinessCombinationStaggeredLockUpArrangementSharesVestingPercent_019e8332-cddb-7b33-a500-f8e377371b7e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_019e8332-cddb-7f8a-95f3-d76cae31af68" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationAcquisitionRelatedCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7c02-b12e-cd647bbfde78" xlink:to="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_019e8332-cddb-7f8a-95f3-d76cae31af68" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts_019e8332-cddb-7472-ba87-04e964f515e1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7c02-b12e-cd647bbfde78" xlink:to="loc_us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts_019e8332-cddb-7472-ba87-04e964f515e1" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationIndemnificationAssetsAmountAsOfAcquisitionDate_019e8332-cddb-7301-a5b9-88f333c5e5c6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationIndemnificationAssetsAmountAsOfAcquisitionDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7c02-b12e-cd647bbfde78" xlink:to="loc_us-gaap_BusinessCombinationIndemnificationAssetsAmountAsOfAcquisitionDate_019e8332-cddb-7301-a5b9-88f333c5e5c6" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_BusinessCombinationIndemnificationLiabilitiesAmount_019e8332-cddb-7f44-9b1c-24d9e163cb22" xlink:href="oust-20260630.xsd#oust_BusinessCombinationIndemnificationLiabilitiesAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7c02-b12e-cd647bbfde78" xlink:to="loc_oust_BusinessCombinationIndemnificationLiabilitiesAmount_019e8332-cddb-7f44-9b1c-24d9e163cb22" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/BusinessCombinationandRelatedTransactionsScheduleofConsiderationPaidDetails" xlink:type="simple" xlink:href="oust-20260630.xsd#BusinessCombinationandRelatedTransactionsScheduleofConsiderationPaidDetails"/>
  <link:definitionLink xlink:role="http://ouster.com/role/BusinessCombinationandRelatedTransactionsScheduleofConsiderationPaidDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7b1a-a052-3fb276806d85" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019e8332-cddb-707f-b348-fe57ae0757bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7b1a-a052-3fb276806d85" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019e8332-cddb-707f-b348-fe57ae0757bd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddb-7869-82b5-91b9ee03d10d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019e8332-cddb-707f-b348-fe57ae0757bd" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddb-7869-82b5-91b9ee03d10d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddb-7869-82b5-91b9ee03d10d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddb-7869-82b5-91b9ee03d10d" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddb-7869-82b5-91b9ee03d10d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddb-735c-acf5-560d43f0bc23" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddb-7869-82b5-91b9ee03d10d" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddb-735c-acf5-560d43f0bc23" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_StereoLabsMember_019e8332-cddb-7ff5-9793-df21df8810a5" xlink:href="oust-20260630.xsd#oust_StereoLabsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddb-735c-acf5-560d43f0bc23" xlink:to="loc_oust_StereoLabsMember_019e8332-cddb-7ff5-9793-df21df8810a5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_019e8332-cddb-7e94-8787-04014fda2fd1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7b1a-a052-3fb276806d85" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_019e8332-cddb-7e94-8787-04014fda2fd1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionEquityInterestIssuedOrIssuableValueAssigned_019e8332-cddb-7fd6-b68d-ec5fc861886e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionEquityInterestIssuedOrIssuableValueAssigned"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7b1a-a052-3fb276806d85" xlink:to="loc_us-gaap_BusinessAcquisitionEquityInterestIssuedOrIssuableValueAssigned_019e8332-cddb-7fd6-b68d-ec5fc861886e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_019e8332-cddb-70ed-9163-e5e1f1220fd0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7b1a-a052-3fb276806d85" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_019e8332-cddb-70ed-9163-e5e1f1220fd0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_019e8332-cddb-7851-9893-aa1505d3ef61" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7b1a-a052-3fb276806d85" xlink:to="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_019e8332-cddb-7851-9893-aa1505d3ef61" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionSharePrice_019e8332-cddb-792f-ba45-b649e04baabb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionSharePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7b1a-a052-3fb276806d85" xlink:to="loc_us-gaap_BusinessAcquisitionSharePrice_019e8332-cddb-792f-ba45-b649e04baabb" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/BusinessCombinationandRelatedTransactionsScheduleofAssetsAcquiredandLiabilitiesAssumedDetails" xlink:type="simple" xlink:href="oust-20260630.xsd#BusinessCombinationandRelatedTransactionsScheduleofAssetsAcquiredandLiabilitiesAssumedDetails"/>
  <link:definitionLink xlink:role="http://ouster.com/role/BusinessCombinationandRelatedTransactionsScheduleofAssetsAcquiredandLiabilitiesAssumedDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7bb0-836b-9ab8feb5ae78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019e8332-cddb-7eb7-ba89-05bd902c94ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7bb0-836b-9ab8feb5ae78" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019e8332-cddb-7eb7-ba89-05bd902c94ff" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddb-7ca4-ba71-5b686aa6f898" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019e8332-cddb-7eb7-ba89-05bd902c94ff" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddb-7ca4-ba71-5b686aa6f898" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddb-7ca4-ba71-5b686aa6f898_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddb-7ca4-ba71-5b686aa6f898" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddb-7ca4-ba71-5b686aa6f898_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddb-7ea1-95a3-7b847270c2f5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddb-7ca4-ba71-5b686aa6f898" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddb-7ea1-95a3-7b847270c2f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_StereoLabsMember_019e8332-cddb-7b80-a756-c7d295f0c8c1" xlink:href="oust-20260630.xsd#oust_StereoLabsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddb-7ea1-95a3-7b847270c2f5" xlink:to="loc_oust_StereoLabsMember_019e8332-cddb-7b80-a756-c7d295f0c8c1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_019e8332-cddb-7cb5-a476-9257226ff819" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7bb0-836b-9ab8feb5ae78" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_019e8332-cddb-7cb5-a476-9257226ff819" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_019e8332-cddb-71ba-8e88-8c7347e20eb3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7bb0-836b-9ab8feb5ae78" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_019e8332-cddb-71ba-8e88-8c7347e20eb3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_019e8332-cddb-7571-91a0-91beeaa89ac9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_019e8332-cddb-71ba-8e88-8c7347e20eb3" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_019e8332-cddb-7571-91a0-91beeaa89ac9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_019e8332-cddb-7bf7-8770-8ed76a06f2a6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_019e8332-cddb-71ba-8e88-8c7347e20eb3" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_019e8332-cddb-7bf7-8770-8ed76a06f2a6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_019e8332-cddb-7e43-914d-50354053855a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_019e8332-cddb-71ba-8e88-8c7347e20eb3" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_019e8332-cddb-7e43-914d-50354053855a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets_019e8332-cddb-7634-bda6-4c864cf53efe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_019e8332-cddb-71ba-8e88-8c7347e20eb3" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets_019e8332-cddb-7634-bda6-4c864cf53efe" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_019e8332-cddb-7a9b-92a0-0cbdf9bac9c4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_019e8332-cddb-71ba-8e88-8c7347e20eb3" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_019e8332-cddb-7a9b-92a0-0cbdf9bac9c4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseRightOfUseAssets_019e8332-cddb-7728-9d59-c1eec0c9e993" xlink:href="oust-20260630.xsd#oust_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseRightOfUseAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_019e8332-cddb-71ba-8e88-8c7347e20eb3" xlink:to="loc_oust_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseRightOfUseAssets_019e8332-cddb-7728-9d59-c1eec0c9e993" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_019e8332-cddb-775d-a6cc-1975ba53b877" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_019e8332-cddb-71ba-8e88-8c7347e20eb3" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_019e8332-cddb-775d-a6cc-1975ba53b877" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets_019e8332-cddb-740f-8159-580bf50656d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_019e8332-cddb-71ba-8e88-8c7347e20eb3" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets_019e8332-cddb-740f-8159-580bf50656d8" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable_019e8332-cddb-7dfc-93a7-7eb0e5458f9b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_019e8332-cddb-71ba-8e88-8c7347e20eb3" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable_019e8332-cddb-7dfc-93a7-7eb0e5458f9b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAccruedAndOtherCurrentLiabilities_019e8332-cddb-72e4-9045-daf9501e7570" xlink:href="oust-20260630.xsd#oust_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAccruedAndOtherCurrentLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_019e8332-cddb-71ba-8e88-8c7347e20eb3" xlink:to="loc_oust_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAccruedAndOtherCurrentLiabilities_019e8332-cddb-72e4-9045-daf9501e7570" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedContractWithCustomerLiabilityCurrent_019e8332-cddb-77c0-ab72-bde4392f6966" xlink:href="oust-20260630.xsd#oust_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_019e8332-cddb-71ba-8e88-8c7347e20eb3" xlink:to="loc_oust_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedContractWithCustomerLiabilityCurrent_019e8332-cddb-77c0-ab72-bde4392f6966" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseLiabilityCurrent_019e8332-cddb-7160-aec9-c1ca63f870b1" xlink:href="oust-20260630.xsd#oust_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_019e8332-cddb-71ba-8e88-8c7347e20eb3" xlink:to="loc_oust_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseLiabilityCurrent_019e8332-cddb-7160-aec9-c1ca63f870b1" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseLiabilityNoncurrent_019e8332-cddb-782f-a31b-e7dc1fdfb887" xlink:href="oust-20260630.xsd#oust_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_019e8332-cddb-71ba-8e88-8c7347e20eb3" xlink:to="loc_oust_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseLiabilityNoncurrent_019e8332-cddb-782f-a31b-e7dc1fdfb887" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities_019e8332-cddb-7016-a0b8-d2e104562e77" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_019e8332-cddb-71ba-8e88-8c7347e20eb3" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities_019e8332-cddb-7016-a0b8-d2e104562e77" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet_019e8332-cddb-7d21-8568-13392f8b2673" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7bb0-836b-9ab8feb5ae78" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet_019e8332-cddb-7d21-8568-13392f8b2673" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019e8332-cddb-78ca-8e19-73201ecf31c4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7bb0-836b-9ab8feb5ae78" xlink:to="loc_us-gaap_Goodwill_019e8332-cddb-78ca-8e19-73201ecf31c4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_019e8332-cddb-70b2-b70d-d50565f7fb29" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7bb0-836b-9ab8feb5ae78" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_019e8332-cddb-70b2-b70d-d50565f7fb29" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationIndemnificationAssetsAmountAsOfAcquisitionDate_019e8332-cddb-748a-9588-453f08663259" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationIndemnificationAssetsAmountAsOfAcquisitionDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7bb0-836b-9ab8feb5ae78" xlink:to="loc_us-gaap_BusinessCombinationIndemnificationAssetsAmountAsOfAcquisitionDate_019e8332-cddb-748a-9588-453f08663259" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_BusinessCombinationIndemnificationLiabilitiesAmount_019e8332-cddb-7bdd-8605-53b79ff4c15f" xlink:href="oust-20260630.xsd#oust_BusinessCombinationIndemnificationLiabilitiesAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7bb0-836b-9ab8feb5ae78" xlink:to="loc_oust_BusinessCombinationIndemnificationLiabilitiesAmount_019e8332-cddb-7bdd-8605-53b79ff4c15f" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/BusinessCombinationandRelatedTransactionsScheduleofAcquiredIndefiniteLivedIntangibleAssetsbyMajorClassDetails" xlink:type="simple" xlink:href="oust-20260630.xsd#BusinessCombinationandRelatedTransactionsScheduleofAcquiredIndefiniteLivedIntangibleAssetsbyMajorClassDetails"/>
  <link:definitionLink xlink:role="http://ouster.com/role/BusinessCombinationandRelatedTransactionsScheduleofAcquiredIndefiniteLivedIntangibleAssetsbyMajorClassDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7583-9de4-599fd3bd002d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019e8332-cddb-74c2-8f97-d56579ead5ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7583-9de4-599fd3bd002d" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019e8332-cddb-74c2-8f97-d56579ead5ff" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddb-75f3-95a1-ca1d89a2c17b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019e8332-cddb-74c2-8f97-d56579ead5ff" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddb-75f3-95a1-ca1d89a2c17b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddb-75f3-95a1-ca1d89a2c17b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddb-75f3-95a1-ca1d89a2c17b" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddb-75f3-95a1-ca1d89a2c17b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddb-7f5f-ac68-0ac5771bb7eb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddb-75f3-95a1-ca1d89a2c17b" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddb-7f5f-ac68-0ac5771bb7eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_StereoLabsMember_019e8332-cddb-78a2-97c0-fef32fa413a5" xlink:href="oust-20260630.xsd#oust_StereoLabsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddb-7f5f-ac68-0ac5771bb7eb" xlink:to="loc_oust_StereoLabsMember_019e8332-cddb-78a2-97c0-fef32fa413a5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019e8332-cddb-76fa-aaca-a702e72c0443" 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_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019e8332-cddb-74c2-8f97-d56579ead5ff" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019e8332-cddb-76fa-aaca-a702e72c0443" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e8332-cddb-76fa-aaca-a702e72c0443_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_019e8332-cddb-76fa-aaca-a702e72c0443" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e8332-cddb-76fa-aaca-a702e72c0443_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e8332-cddb-7b12-a160-449f1cdca84e" 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_019e8332-cddb-76fa-aaca-a702e72c0443" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e8332-cddb-7b12-a160-449f1cdca84e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradeNamesMember_019e8332-cddb-76dc-8039-63768d8b312d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e8332-cddb-7b12-a160-449f1cdca84e" xlink:to="loc_us-gaap_TradeNamesMember_019e8332-cddb-76dc-8039-63768d8b312d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_DevelopedTechnologySoftwareMember_019e8332-cddb-7982-ba33-e3bbbee16e06" xlink:href="oust-20260630.xsd#oust_DevelopedTechnologySoftwareMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e8332-cddb-7b12-a160-449f1cdca84e" xlink:to="loc_oust_DevelopedTechnologySoftwareMember_019e8332-cddb-7982-ba33-e3bbbee16e06" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_019e8332-cddb-7dd4-b6ac-2a8228ce58ce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e8332-cddb-7b12-a160-449f1cdca84e" xlink:to="loc_us-gaap_CustomerRelationshipsMember_019e8332-cddb-7dd4-b6ac-2a8228ce58ce" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_019e8332-cddb-754b-a5e7-ffc3e635c7c4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7583-9de4-599fd3bd002d" xlink:to="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_019e8332-cddb-754b-a5e7-ffc3e635c7c4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_019e8332-cddb-700f-9932-d5e2091f89e3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7583-9de4-599fd3bd002d" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_019e8332-cddb-700f-9932-d5e2091f89e3" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/BusinessCombinationandRelatedTransactionsScheduleofBusinessAcquisitionProFormaInformationDetails" xlink:type="simple" xlink:href="oust-20260630.xsd#BusinessCombinationandRelatedTransactionsScheduleofBusinessAcquisitionProFormaInformationDetails"/>
  <link:definitionLink xlink:role="http://ouster.com/role/BusinessCombinationandRelatedTransactionsScheduleofBusinessAcquisitionProFormaInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-778c-8aa0-922718602634" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019e8332-cddb-7f33-b748-1469f55baabd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-778c-8aa0-922718602634" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019e8332-cddb-7f33-b748-1469f55baabd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddb-7fba-9e5e-ff27d9a659e2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019e8332-cddb-7f33-b748-1469f55baabd" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddb-7fba-9e5e-ff27d9a659e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddb-7fba-9e5e-ff27d9a659e2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddb-7fba-9e5e-ff27d9a659e2" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddb-7fba-9e5e-ff27d9a659e2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddb-75ca-9476-9c44a9ef2a45" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddb-7fba-9e5e-ff27d9a659e2" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddb-75ca-9476-9c44a9ef2a45" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_StereoLabsMember_019e8332-cddb-7e5e-8371-43adc54a3d76" xlink:href="oust-20260630.xsd#oust_StereoLabsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddb-75ca-9476-9c44a9ef2a45" xlink:to="loc_oust_StereoLabsMember_019e8332-cddb-7e5e-8371-43adc54a3d76" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionsProFormaRevenue_019e8332-cddb-7a27-9ac2-29ad3371f798" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionsProFormaRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-778c-8aa0-922718602634" xlink:to="loc_us-gaap_BusinessAcquisitionsProFormaRevenue_019e8332-cddb-7a27-9ac2-29ad3371f798" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss_019e8332-cddb-7077-8839-18a0bf240a71" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-778c-8aa0-922718602634" xlink:to="loc_us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss_019e8332-cddb-7077-8839-18a0bf240a71" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/BusinessCombinationandRelatedTransactionsScheduleofProFormaInformationAdjustmentsDetails" xlink:type="simple" xlink:href="oust-20260630.xsd#BusinessCombinationandRelatedTransactionsScheduleofProFormaInformationAdjustmentsDetails"/>
  <link:definitionLink xlink:role="http://ouster.com/role/BusinessCombinationandRelatedTransactionsScheduleofProFormaInformationAdjustmentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7d3f-a19d-812ff8065fa8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019e8332-cddb-7ce6-b7b1-bbd1d8107f75" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7d3f-a19d-812ff8065fa8" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019e8332-cddb-7ce6-b7b1-bbd1d8107f75" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddb-7f7c-a57d-ba34d6892e0e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019e8332-cddb-7ce6-b7b1-bbd1d8107f75" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddb-7f7c-a57d-ba34d6892e0e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddb-7f7c-a57d-ba34d6892e0e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddb-7f7c-a57d-ba34d6892e0e" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddb-7f7c-a57d-ba34d6892e0e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddb-70af-b858-c6dd6e1bf1ec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddb-7f7c-a57d-ba34d6892e0e" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddb-70af-b858-c6dd6e1bf1ec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_StereoLabsMember_019e8332-cddb-7f03-a027-54d357097ec4" xlink:href="oust-20260630.xsd#oust_StereoLabsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddb-70af-b858-c6dd6e1bf1ec" xlink:to="loc_oust_StereoLabsMember_019e8332-cddb-7f03-a027-54d357097ec4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonrecurringAdjustmentAxis_019e8332-cddb-7818-ad31-e84a6b028ba5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonrecurringAdjustmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019e8332-cddb-7ce6-b7b1-bbd1d8107f75" xlink:to="loc_us-gaap_NonrecurringAdjustmentAxis_019e8332-cddb-7818-ad31-e84a6b028ba5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonrecurringAdjustmentDomain_019e8332-cddb-7818-ad31-e84a6b028ba5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonrecurringAdjustmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_NonrecurringAdjustmentAxis_019e8332-cddb-7818-ad31-e84a6b028ba5" xlink:to="loc_us-gaap_NonrecurringAdjustmentDomain_019e8332-cddb-7818-ad31-e84a6b028ba5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonrecurringAdjustmentDomain_019e8332-cddb-7c28-9d86-a34c71ef66c6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonrecurringAdjustmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_NonrecurringAdjustmentAxis_019e8332-cddb-7818-ad31-e84a6b028ba5" xlink:to="loc_us-gaap_NonrecurringAdjustmentDomain_019e8332-cddb-7c28-9d86-a34c71ef66c6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_FairValueAdjustmentToIntangibleAssetsMember_019e8332-cddb-7b2b-b2a7-3dc9564ae937" xlink:href="oust-20260630.xsd#oust_FairValueAdjustmentToIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonrecurringAdjustmentDomain_019e8332-cddb-7c28-9d86-a34c71ef66c6" xlink:to="loc_oust_FairValueAdjustmentToIntangibleAssetsMember_019e8332-cddb-7b2b-b2a7-3dc9564ae937" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquisitionRelatedCostsMember_019e8332-cddb-797b-b732-64658eeaba7b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AcquisitionRelatedCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonrecurringAdjustmentDomain_019e8332-cddb-7c28-9d86-a34c71ef66c6" xlink:to="loc_us-gaap_AcquisitionRelatedCostsMember_019e8332-cddb-797b-b732-64658eeaba7b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_BusinessCombinationProFormaInformationNonrecurringAdjustmentSellerAcquisitionRelatedCostMember_019e8332-cddb-746d-bc6d-d52740ba7f2e" xlink:href="oust-20260630.xsd#oust_BusinessCombinationProFormaInformationNonrecurringAdjustmentSellerAcquisitionRelatedCostMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquisitionRelatedCostsMember_019e8332-cddb-797b-b732-64658eeaba7b" xlink:to="loc_oust_BusinessCombinationProFormaInformationNonrecurringAdjustmentSellerAcquisitionRelatedCostMember_019e8332-cddb-746d-bc6d-d52740ba7f2e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_ShareBasedCompensationExpenseAdjustmentMember_019e8332-cddb-7577-bb89-68bf8958ebb0" xlink:href="oust-20260630.xsd#oust_ShareBasedCompensationExpenseAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonrecurringAdjustmentDomain_019e8332-cddb-7c28-9d86-a34c71ef66c6" xlink:to="loc_oust_ShareBasedCompensationExpenseAdjustmentMember_019e8332-cddb-7577-bb89-68bf8958ebb0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_AdjustmentToExpensesRelatedToVestingOfWarrantMember_019e8332-cddb-71a3-b1dc-deddde388509" xlink:href="oust-20260630.xsd#oust_AdjustmentToExpensesRelatedToVestingOfWarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonrecurringAdjustmentDomain_019e8332-cddb-7c28-9d86-a34c71ef66c6" xlink:to="loc_oust_AdjustmentToExpensesRelatedToVestingOfWarrantMember_019e8332-cddb-71a3-b1dc-deddde388509" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss_019e8332-cddb-7423-8e34-d102e8cc9033" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7d3f-a19d-812ff8065fa8" xlink:to="loc_us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss_019e8332-cddb-7423-8e34-d102e8cc9033" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts_019f7041-2f36-71df-b2e4-24f4b8b2ba1b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddb-7d3f-a19d-812ff8065fa8" xlink:to="loc_us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts_019f7041-2f36-71df-b2e4-24f4b8b2ba1b" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/FairValueofFinancialInstrumentsScheduleofFairValueAssetsandLiabilitiesMeasuredonRecurringBasisDetails" xlink:type="simple" xlink:href="oust-20260630.xsd#FairValueofFinancialInstrumentsScheduleofFairValueAssetsandLiabilitiesMeasuredonRecurringBasisDetails"/>
  <link:definitionLink xlink:role="http://ouster.com/role/FairValueofFinancialInstrumentsScheduleofFairValueAssetsandLiabilitiesMeasuredonRecurringBasisDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019e8332-cddc-7d66-b809-e22aa8028843" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019e8332-cddb-710a-b965-56ef9049d9b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019e8332-cddc-7d66-b809-e22aa8028843" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019e8332-cddb-710a-b965-56ef9049d9b4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAxis_019e8332-cddb-78fc-99ff-837f36a8633f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019e8332-cddb-710a-b965-56ef9049d9b4" xlink:to="loc_us-gaap_CashAndCashEquivalentsAxis_019e8332-cddb-78fc-99ff-837f36a8633f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019e8332-cddb-78fc-99ff-837f36a8633f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_019e8332-cddb-78fc-99ff-837f36a8633f" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019e8332-cddb-78fc-99ff-837f36a8633f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019e8332-cddb-7bc9-a0c5-c723ba33a765" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_019e8332-cddb-78fc-99ff-837f36a8633f" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019e8332-cddb-7bc9-a0c5-c723ba33a765" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_019e8332-cddb-753d-b877-ae3a19f5164d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019e8332-cddb-7bc9-a0c5-c723ba33a765" xlink:to="loc_us-gaap_MoneyMarketFundsMember_019e8332-cddb-753d-b877-ae3a19f5164d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e8332-cddb-7725-bcda-a56e46810149" 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_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019e8332-cddb-710a-b965-56ef9049d9b4" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e8332-cddb-7725-bcda-a56e46810149" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e8332-cddb-7725-bcda-a56e46810149_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_019e8332-cddb-7725-bcda-a56e46810149" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e8332-cddb-7725-bcda-a56e46810149_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e8332-cddb-7801-b766-ae693097b2aa" 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_019e8332-cddb-7725-bcda-a56e46810149" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e8332-cddb-7801-b766-ae693097b2aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019e8332-cddb-749d-a358-8f465650382c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e8332-cddb-7801-b766-ae693097b2aa" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019e8332-cddb-749d-a358-8f465650382c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019e8332-cddc-7a12-90c9-f99acc4e283f" 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_019e8332-cddb-7801-b766-ae693097b2aa" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019e8332-cddc-7a12-90c9-f99acc4e283f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019e8332-cddc-7120-b6f4-b09ed653b68a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019e8332-cddb-710a-b965-56ef9049d9b4" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019e8332-cddc-7120-b6f4-b09ed653b68a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019e8332-cddc-7120-b6f4-b09ed653b68a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019e8332-cddc-7120-b6f4-b09ed653b68a" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019e8332-cddc-7120-b6f4-b09ed653b68a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019e8332-cddc-799d-81c9-2d4cdaf1b4e2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019e8332-cddc-7120-b6f4-b09ed653b68a" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019e8332-cddc-799d-81c9-2d4cdaf1b4e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaperMember_019e8332-cddc-769c-b054-d6f68dc61cb4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialPaperMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019e8332-cddc-799d-81c9-2d4cdaf1b4e2" xlink:to="loc_us-gaap_CommercialPaperMember_019e8332-cddc-769c-b054-d6f68dc61cb4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_019e8332-cddc-7aaf-b630-1d54fdaf7cdf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019e8332-cddc-799d-81c9-2d4cdaf1b4e2" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_019e8332-cddc-7aaf-b630-1d54fdaf7cdf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosureAbstract_019e8332-cddc-76c8-b66f-f49c0025c398" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019e8332-cddc-7d66-b809-e22aa8028843" xlink:to="loc_us-gaap_AssetsFairValueDisclosureAbstract_019e8332-cddc-76c8-b66f-f49c0025c398" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_019e8332-cddc-79eb-8728-525b01bd649f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_019e8332-cddc-76c8-b66f-f49c0025c398" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_019e8332-cddc-79eb-8728-525b01bd649f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterestCurrent_019e8332-cddc-7a82-8a89-48510e81a20c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterestCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_019e8332-cddc-76c8-b66f-f49c0025c398" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterestCurrent_019e8332-cddc-7a82-8a89-48510e81a20c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_019e8332-cddc-78ba-92d8-3c6254cf8798" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_019e8332-cddc-76c8-b66f-f49c0025c398" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_019e8332-cddc-78ba-92d8-3c6254cf8798" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/BalanceSheetComponentsScheduleofCashandCashEquivalentsDetails" xlink:type="simple" xlink:href="oust-20260630.xsd#BalanceSheetComponentsScheduleofCashandCashEquivalentsDetails"/>
  <link:definitionLink xlink:role="http://ouster.com/role/BalanceSheetComponentsScheduleofCashandCashEquivalentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsLineItems_019e8332-cddc-7a98-a8b9-17716d0e45a7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTable_019e8332-cddc-7d51-905f-f0dca7094957" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfCashAndCashEquivalentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_019e8332-cddc-7a98-a8b9-17716d0e45a7" xlink:to="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTable_019e8332-cddc-7d51-905f-f0dca7094957" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAxis_019e8332-cddc-7cca-a4f9-6b7d11de5e5e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTable_019e8332-cddc-7d51-905f-f0dca7094957" xlink:to="loc_us-gaap_CashAndCashEquivalentsAxis_019e8332-cddc-7cca-a4f9-6b7d11de5e5e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019e8332-cddc-7cca-a4f9-6b7d11de5e5e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_019e8332-cddc-7cca-a4f9-6b7d11de5e5e" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019e8332-cddc-7cca-a4f9-6b7d11de5e5e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019e8332-cddc-7336-8c33-eb1c9e2862f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_019e8332-cddc-7cca-a4f9-6b7d11de5e5e" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019e8332-cddc-7336-8c33-eb1c9e2862f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_019e8332-cddc-7772-8700-e5be8e2236df" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019e8332-cddc-7336-8c33-eb1c9e2862f3" xlink:to="loc_us-gaap_MoneyMarketFundsMember_019e8332-cddc-7772-8700-e5be8e2236df" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Cash_019e8332-cddc-7d8c-8dbc-0dca8d154392" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Cash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_019e8332-cddc-7a98-a8b9-17716d0e45a7" xlink:to="loc_us-gaap_Cash_019e8332-cddc-7d8c-8dbc-0dca8d154392" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashEquivalentsAtCarryingValue_019e8332-cddc-7c77-9fcf-11fbb9615fe6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_019e8332-cddc-7a98-a8b9-17716d0e45a7" xlink:to="loc_us-gaap_CashEquivalentsAtCarryingValue_019e8332-cddc-7c77-9fcf-11fbb9615fe6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019e8332-cddc-7448-bc5d-b4420a9afd32" 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_CashAndCashEquivalentsLineItems_019e8332-cddc-7a98-a8b9-17716d0e45a7" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019e8332-cddc-7448-bc5d-b4420a9afd32" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/BalanceSheetComponentsScheduleofPrepaidExpensesandOtherCurrentAssetsDetails" xlink:type="simple" xlink:href="oust-20260630.xsd#BalanceSheetComponentsScheduleofPrepaidExpensesandOtherCurrentAssetsDetails"/>
  <link:definitionLink xlink:role="http://ouster.com/role/BalanceSheetComponentsScheduleofPrepaidExpensesandOtherCurrentAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddc-71f3-938b-da0be8294a76" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019e8332-cddc-7ddf-baee-fff37f867fd6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddc-71f3-938b-da0be8294a76" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019e8332-cddc-7ddf-baee-fff37f867fd6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddc-7d86-a58c-35b78c1f4152" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019e8332-cddc-7ddf-baee-fff37f867fd6" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddc-7d86-a58c-35b78c1f4152" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddc-7d86-a58c-35b78c1f4152_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddc-7d86-a58c-35b78c1f4152" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddc-7d86-a58c-35b78c1f4152_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddc-7527-b8a1-0a572066a262" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddc-7d86-a58c-35b78c1f4152" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddc-7527-b8a1-0a572066a262" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_StereoLabsMember_019e8332-cddc-719b-bbf3-8fc3b67f0729" xlink:href="oust-20260630.xsd#oust_StereoLabsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddc-7527-b8a1-0a572066a262" xlink:to="loc_oust_StereoLabsMember_019e8332-cddc-719b-bbf3-8fc3b67f0729" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainContingenciesByNatureAxis_019f8fc8-74e8-7f3f-8e3f-88ff21891132" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainContingenciesByNatureAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019e8332-cddc-7ddf-baee-fff37f867fd6" xlink:to="loc_us-gaap_GainContingenciesByNatureAxis_019f8fc8-74e8-7f3f-8e3f-88ff21891132" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainContingencyNatureDomain_019f8fc8-74e8-7f3f-8e3f-88ff21891132_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_GainContingenciesByNatureAxis_019f8fc8-74e8-7f3f-8e3f-88ff21891132" xlink:to="loc_us-gaap_GainContingencyNatureDomain_019f8fc8-74e8-7f3f-8e3f-88ff21891132_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainContingencyNatureDomain_019f8fc8-74e8-7fc9-b272-7d543f3cbfa8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_GainContingenciesByNatureAxis_019f8fc8-74e8-7f3f-8e3f-88ff21891132" xlink:to="loc_us-gaap_GainContingencyNatureDomain_019f8fc8-74e8-7fc9-b272-7d543f3cbfa8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_IEEPATariffRefundMember_019f8fc8-74e8-79a9-a9f7-e7a4611dcd9d" xlink:href="oust-20260630.xsd#oust_IEEPATariffRefundMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GainContingencyNatureDomain_019f8fc8-74e8-7fc9-b272-7d543f3cbfa8" xlink:to="loc_oust_IEEPATariffRefundMember_019f8fc8-74e8-79a9-a9f7-e7a4611dcd9d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPrepaidExpenseCurrent_019e8332-cddc-7113-af93-282fdd1946ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherPrepaidExpenseCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddc-71f3-938b-da0be8294a76" xlink:to="loc_us-gaap_OtherPrepaidExpenseCurrent_019e8332-cddc-7113-af93-282fdd1946ef" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_PrepaidInventory_019e8332-cddc-72aa-8b48-fb1143576156" xlink:href="oust-20260630.xsd#oust_PrepaidInventory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddc-71f3-938b-da0be8294a76" xlink:to="loc_oust_PrepaidInventory_019e8332-cddc-72aa-8b48-fb1143576156" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidInsurance_019e8332-cddc-70a1-b14a-2cbdcc4f2f8d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PrepaidInsurance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddc-71f3-938b-da0be8294a76" xlink:to="loc_us-gaap_PrepaidInsurance_019e8332-cddc-70a1-b14a-2cbdcc4f2f8d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_ReceivableFromContractManufacturerCurrent_019e8332-cddc-778c-80e1-5e5ddbfeaee7" xlink:href="oust-20260630.xsd#oust_ReceivableFromContractManufacturerCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddc-71f3-938b-da0be8294a76" xlink:to="loc_oust_ReceivableFromContractManufacturerCurrent_019e8332-cddc-778c-80e1-5e5ddbfeaee7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_ReceivableForRecoveryOfImportDutiesAndAccruedInterestNet_019f7045-0929-78c9-9711-e03de083d1db" xlink:href="oust-20260630.xsd#oust_ReceivableForRecoveryOfImportDutiesAndAccruedInterestNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddc-71f3-938b-da0be8294a76" xlink:to="loc_oust_ReceivableForRecoveryOfImportDutiesAndAccruedInterestNet_019f7045-0929-78c9-9711-e03de083d1db" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxesReceivable_019e8332-cddc-740d-9501-8f4e397dae54" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxesReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddc-71f3-938b-da0be8294a76" xlink:to="loc_us-gaap_IncomeTaxesReceivable_019e8332-cddc-740d-9501-8f4e397dae54" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationIndemnificationAssetsAmountAsOfAcquisitionDate_019e8332-cddc-78e8-a682-2fecd8babe71" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationIndemnificationAssetsAmountAsOfAcquisitionDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddc-71f3-938b-da0be8294a76" xlink:to="loc_us-gaap_BusinessCombinationIndemnificationAssetsAmountAsOfAcquisitionDate_019e8332-cddc-78e8-a682-2fecd8babe71" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsCurrent_019e8332-cddc-7e0e-ab48-cb792d4e02d6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddc-71f3-938b-da0be8294a76" xlink:to="loc_us-gaap_OtherAssetsCurrent_019e8332-cddc-7e0e-ab48-cb792d4e02d6" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_019e8332-cddc-79a8-9aff-c573eac6a56a" 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_BusinessAcquisitionLineItems_019e8332-cddc-71f3-938b-da0be8294a76" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_019e8332-cddc-79a8-9aff-c573eac6a56a" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/BalanceSheetComponentsScheduleofPropertyPlantandEquipmentDetails" xlink:type="simple" xlink:href="oust-20260630.xsd#BalanceSheetComponentsScheduleofPropertyPlantandEquipmentDetails"/>
  <link:definitionLink xlink:role="http://ouster.com/role/BalanceSheetComponentsScheduleofPropertyPlantandEquipmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e8332-cddc-7237-b172-03aa19f9894d" 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_019e8332-cddc-723c-9389-b9ac36556b7b" 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_019e8332-cddc-7237-b172-03aa19f9894d" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019e8332-cddc-723c-9389-b9ac36556b7b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e8332-cddc-7b2d-b182-3db9e952ad72" 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_019e8332-cddc-723c-9389-b9ac36556b7b" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e8332-cddc-7b2d-b182-3db9e952ad72" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e8332-cddc-7b2d-b182-3db9e952ad72_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_019e8332-cddc-7b2d-b182-3db9e952ad72" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e8332-cddc-7b2d-b182-3db9e952ad72_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e8332-cddc-7db4-ba02-e3560edd7cb5" 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_019e8332-cddc-7b2d-b182-3db9e952ad72" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e8332-cddc-7db4-ba02-e3560edd7cb5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LandMember_019e8332-cddc-777a-b567-957bcbcffe8c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LandMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e8332-cddc-7db4-ba02-e3560edd7cb5" xlink:to="loc_us-gaap_LandMember_019e8332-cddc-777a-b567-957bcbcffe8c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BuildingMember_019e8332-cddc-75d8-9e64-38a5ae5ae2fc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BuildingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e8332-cddc-7db4-ba02-e3560edd7cb5" xlink:to="loc_us-gaap_BuildingMember_019e8332-cddc-75d8-9e64-38a5ae5ae2fc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MachineryAndEquipmentMember_019e8332-cddc-793f-9457-d507e569b5e6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MachineryAndEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e8332-cddc-7db4-ba02-e3560edd7cb5" xlink:to="loc_us-gaap_MachineryAndEquipmentMember_019e8332-cddc-793f-9457-d507e569b5e6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComputerEquipmentMember_019e8332-cddc-7d51-858b-60d647f83b31" 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_019e8332-cddc-7db4-ba02-e3560edd7cb5" xlink:to="loc_us-gaap_ComputerEquipmentMember_019e8332-cddc-7d51-858b-60d647f83b31" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VehiclesMember_019e8332-cddc-7545-ad2f-ef5b72766348" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VehiclesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e8332-cddc-7db4-ba02-e3560edd7cb5" xlink:to="loc_us-gaap_VehiclesMember_019e8332-cddc-7545-ad2f-ef5b72766348" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_019e8332-cddc-79ad-9bc1-6b6b5bb4251a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SoftwareAndSoftwareDevelopmentCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e8332-cddc-7db4-ba02-e3560edd7cb5" xlink:to="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_019e8332-cddc-79ad-9bc1-6b6b5bb4251a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_019e8332-cddc-75e8-8d6a-d6441603cefc" 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_019e8332-cddc-7db4-ba02-e3560edd7cb5" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_019e8332-cddc-75e8-8d6a-d6441603cefc" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionInProgressMember_019e8332-cddc-7845-9d3f-bf387435df9b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConstructionInProgressMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e8332-cddc-7db4-ba02-e3560edd7cb5" xlink:to="loc_us-gaap_ConstructionInProgressMember_019e8332-cddc-7845-9d3f-bf387435df9b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_019e8332-cddc-7f04-ba70-bcdd6406959b" 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_019e8332-cddc-7db4-ba02-e3560edd7cb5" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_019e8332-cddc-7f04-ba70-bcdd6406959b" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_019e8332-cddc-777c-8fbc-5cb1dd0f2c9a" 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_019e8332-cddc-7237-b172-03aa19f9894d" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_019e8332-cddc-777c-8fbc-5cb1dd0f2c9a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_019e8332-cddc-784e-93d2-11ba5ef4988e" 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_019e8332-cddc-7237-b172-03aa19f9894d" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_019e8332-cddc-784e-93d2-11ba5ef4988e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019e8332-cddc-722f-bea2-db37b1a1b5ff" 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_019e8332-cddc-7237-b172-03aa19f9894d" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019e8332-cddc-722f-bea2-db37b1a1b5ff" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019e8332-cddc-73bd-b865-366db1f13dbb" 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_019e8332-cddc-7237-b172-03aa19f9894d" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019e8332-cddc-73bd-b865-366db1f13dbb" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/BalanceSheetComponentsScheduleofAcquiredIntangibleAssetsDetails" xlink:type="simple" xlink:href="oust-20260630.xsd#BalanceSheetComponentsScheduleofAcquiredIntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://ouster.com/role/BalanceSheetComponentsScheduleofAcquiredIntangibleAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e8332-cddc-7972-b398-f640fdc5721b" 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_019e8332-cddc-7721-ab61-7226f859f74e" 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_019e8332-cddc-7972-b398-f640fdc5721b" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019e8332-cddc-7721-ab61-7226f859f74e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019e8332-cddc-7659-9032-8a192fece642" 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_019e8332-cddc-7721-ab61-7226f859f74e" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019e8332-cddc-7659-9032-8a192fece642" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e8332-cddc-7659-9032-8a192fece642_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_019e8332-cddc-7659-9032-8a192fece642" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e8332-cddc-7659-9032-8a192fece642_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e8332-cddc-7753-b94b-f00baca882a9" 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_019e8332-cddc-7659-9032-8a192fece642" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e8332-cddc-7753-b94b-f00baca882a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradeNamesMember_019e8332-cddc-75ef-a09e-c216650908de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e8332-cddc-7753-b94b-f00baca882a9" xlink:to="loc_us-gaap_TradeNamesMember_019e8332-cddc-75ef-a09e-c216650908de" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TechnologyBasedIntangibleAssetsMember_019e8332-cddc-78cb-b1a6-c2fd5d65f496" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TechnologyBasedIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e8332-cddc-7753-b94b-f00baca882a9" xlink:to="loc_us-gaap_TechnologyBasedIntangibleAssetsMember_019e8332-cddc-78cb-b1a6-c2fd5d65f496" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_VendorRelationshipMember_019e8332-cddc-79eb-afeb-ac241b0bb8ff" xlink:href="oust-20260630.xsd#oust_VendorRelationshipMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e8332-cddc-7753-b94b-f00baca882a9" xlink:to="loc_oust_VendorRelationshipMember_019e8332-cddc-79eb-afeb-ac241b0bb8ff" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_019e8332-cddc-7f96-85c1-0d944756059c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e8332-cddc-7753-b94b-f00baca882a9" xlink:to="loc_us-gaap_CustomerRelationshipsMember_019e8332-cddc-7f96-85c1-0d944756059c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019e8332-cddc-705b-9b50-7bb104857c81" 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_ScheduleOfFiniteLivedIntangibleAssetsTable_019e8332-cddc-7721-ab61-7226f859f74e" xlink:to="loc_srt_RangeAxis_019e8332-cddc-705b-9b50-7bb104857c81" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e8332-cddc-705b-9b50-7bb104857c81_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_019e8332-cddc-705b-9b50-7bb104857c81" xlink:to="loc_srt_RangeMember_019e8332-cddc-705b-9b50-7bb104857c81_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e8332-cddc-7c5e-b285-0179bbfe7e46" 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_019e8332-cddc-705b-9b50-7bb104857c81" xlink:to="loc_srt_RangeMember_019e8332-cddc-7c5e-b285-0179bbfe7e46" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019e8332-cddc-74e4-b778-79de61940624" 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_019e8332-cddc-7c5e-b285-0179bbfe7e46" xlink:to="loc_srt_MinimumMember_019e8332-cddc-74e4-b778-79de61940624" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019e8332-cddc-7845-8149-ef9042280ac9" 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_019e8332-cddc-7c5e-b285-0179bbfe7e46" xlink:to="loc_srt_MaximumMember_019e8332-cddc-7845-8149-ef9042280ac9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_019e8332-cddc-7213-9438-45ffdbdbc7fb" 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_019e8332-cddc-7972-b398-f640fdc5721b" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_019e8332-cddc-7213-9438-45ffdbdbc7fb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_019e8332-cddc-7892-8b36-0fe8bc1c0b1e" 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_019e8332-cddc-7972-b398-f640fdc5721b" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_019e8332-cddc-7892-8b36-0fe8bc1c0b1e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019e8332-cddc-7464-addb-d1d506e692a9" 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_019e8332-cddc-7972-b398-f640fdc5721b" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019e8332-cddc-7464-addb-d1d506e692a9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019e8332-cddc-7023-a8be-e950fe84eaba" 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_019e8332-cddc-7972-b398-f640fdc5721b" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019e8332-cddc-7023-a8be-e950fe84eaba" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/BalanceSheetComponentsScheduleofAccruedandOtherCurrentLiabilitiesDetails" xlink:type="simple" xlink:href="oust-20260630.xsd#BalanceSheetComponentsScheduleofAccruedandOtherCurrentLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://ouster.com/role/BalanceSheetComponentsScheduleofAccruedandOtherCurrentLiabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddc-7d01-ad7e-ea447bbeb048" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019e8332-cddc-7ec4-9d6c-fc4e2ce172a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddc-7d01-ad7e-ea447bbeb048" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019e8332-cddc-7ec4-9d6c-fc4e2ce172a0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddc-744d-a542-4007011eca4b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019e8332-cddc-7ec4-9d6c-fc4e2ce172a0" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddc-744d-a542-4007011eca4b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddc-744d-a542-4007011eca4b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddc-744d-a542-4007011eca4b" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddc-744d-a542-4007011eca4b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddc-75e3-b4fe-a3a458f82fdb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddc-744d-a542-4007011eca4b" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddc-75e3-b4fe-a3a458f82fdb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_StereoLabsMember_019e8332-cddc-7ccc-a0f6-d539a7a9a5cb" xlink:href="oust-20260630.xsd#oust_StereoLabsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddc-75e3-b4fe-a3a458f82fdb" xlink:to="loc_oust_StereoLabsMember_019e8332-cddc-7ccc-a0f6-d539a7a9a5cb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyAccrualCarryingValueCurrent_019e8332-cddc-774d-9372-7c70a60df259" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LossContingencyAccrualCarryingValueCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddc-7d01-ad7e-ea447bbeb048" xlink:to="loc_us-gaap_LossContingencyAccrualCarryingValueCurrent_019e8332-cddc-774d-9372-7c70a60df259" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_UninvoicedReceiptsOtherCurrentLiabilities_019e8332-cddc-7d3d-9af1-32cfe9bb38f7" xlink:href="oust-20260630.xsd#oust_UninvoicedReceiptsOtherCurrentLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddc-7d01-ad7e-ea447bbeb048" xlink:to="loc_oust_UninvoicedReceiptsOtherCurrentLiabilities_019e8332-cddc-7d3d-9af1-32cfe9bb38f7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeRelatedLiabilitiesCurrent_019e8332-cddc-77eb-a7dd-69eb9eb1092f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeRelatedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddc-7d01-ad7e-ea447bbeb048" xlink:to="loc_us-gaap_EmployeeRelatedLiabilitiesCurrent_019e8332-cddc-77eb-a7dd-69eb9eb1092f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StandardProductWarrantyAccrual_019e8332-cddc-72f1-8bac-9197c0b82065" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StandardProductWarrantyAccrual"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddc-7d01-ad7e-ea447bbeb048" xlink:to="loc_us-gaap_StandardProductWarrantyAccrual_019e8332-cddc-72f1-8bac-9197c0b82065" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesAndExciseTaxPayableCurrent_019e8332-cddc-7abc-955b-9e99fec58378" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SalesAndExciseTaxPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddc-7d01-ad7e-ea447bbeb048" xlink:to="loc_us-gaap_SalesAndExciseTaxPayableCurrent_019e8332-cddc-7abc-955b-9e99fec58378" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAccruedLiabilitiesCurrent_019e8332-cddc-7073-aae2-4bb0dfc26ea5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddc-7d01-ad7e-ea447bbeb048" xlink:to="loc_us-gaap_OtherAccruedLiabilitiesCurrent_019e8332-cddc-7073-aae2-4bb0dfc26ea5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_AccruedAndOtherLiabilitiesCurrent_019e8332-cddc-72e9-8110-1738e0dbd6c8" xlink:href="oust-20260630.xsd#oust_AccruedAndOtherLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddc-7d01-ad7e-ea447bbeb048" xlink:to="loc_oust_AccruedAndOtherLiabilitiesCurrent_019e8332-cddc-72e9-8110-1738e0dbd6c8" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_BusinessCombinationIndemnificationLiabilitiesAmount_019e8332-cddc-7760-9e0c-e5ca8db02304" xlink:href="oust-20260630.xsd#oust_BusinessCombinationIndemnificationLiabilitiesAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddc-7d01-ad7e-ea447bbeb048" xlink:to="loc_oust_BusinessCombinationIndemnificationLiabilitiesAmount_019e8332-cddc-7760-9e0c-e5ca8db02304" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationIndemnificationAssetsAmountAsOfAcquisitionDate_019e8332-cddc-785e-8f6b-89747a938836" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationIndemnificationAssetsAmountAsOfAcquisitionDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019e8332-cddc-7d01-ad7e-ea447bbeb048" xlink:to="loc_us-gaap_BusinessCombinationIndemnificationAssetsAmountAsOfAcquisitionDate_019e8332-cddc-785e-8f6b-89747a938836" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/AmazonWarrantDetails" xlink:type="simple" xlink:href="oust-20260630.xsd#AmazonWarrantDetails"/>
  <link:definitionLink xlink:role="http://ouster.com/role/AmazonWarrantDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightLineItems_019e8332-cddc-729b-bd3c-4953aeef42ed" 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_019e8332-cddc-7e9f-8573-9e0f3fc68bd0" 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_019e8332-cddc-729b-bd3c-4953aeef42ed" xlink:to="loc_us-gaap_ClassOfWarrantOrRightTable_019e8332-cddc-7e9f-8573-9e0f3fc68bd0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019e8332-cddc-790e-9066-d6dd4af73f9e" 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_ClassOfWarrantOrRightTable_019e8332-cddc-7e9f-8573-9e0f3fc68bd0" xlink:to="loc_srt_CounterpartyNameAxis_019e8332-cddc-790e-9066-d6dd4af73f9e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e8332-cddc-790e-9066-d6dd4af73f9e_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_019e8332-cddc-790e-9066-d6dd4af73f9e" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e8332-cddc-790e-9066-d6dd4af73f9e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e8332-cddc-798f-b6c7-210253a5213e" 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_019e8332-cddc-790e-9066-d6dd4af73f9e" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e8332-cddc-798f-b6c7-210253a5213e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_AmazoncomNVInvestmentHoldingsLLLCMember_019e8332-cddc-76aa-b0e2-1602eb11d08f" xlink:href="oust-20260630.xsd#oust_AmazoncomNVInvestmentHoldingsLLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e8332-cddc-798f-b6c7-210253a5213e" xlink:to="loc_oust_AmazoncomNVInvestmentHoldingsLLLCMember_019e8332-cddc-76aa-b0e2-1602eb11d08f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddc-75c3-89da-05c62c16f334" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfWarrantOrRightTable_019e8332-cddc-7e9f-8573-9e0f3fc68bd0" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddc-75c3-89da-05c62c16f334" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddc-75c3-89da-05c62c16f334_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddc-75c3-89da-05c62c16f334" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddc-75c3-89da-05c62c16f334_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddc-78e1-a1d8-cc88c815c52e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddc-75c3-89da-05c62c16f334" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddc-78e1-a1d8-cc88c815c52e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_VelodyneLidarIncMember_019e8332-cddc-70c5-8c11-eb7c422d533f" xlink:href="oust-20260630.xsd#oust_VelodyneLidarIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddc-78e1-a1d8-cc88c815c52e" xlink:to="loc_oust_VelodyneLidarIncMember_019e8332-cddc-70c5-8c11-eb7c422d533f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_StereolabsAcquisitionMember_019e8332-cddc-7a73-932d-61d309b87957" xlink:href="oust-20260630.xsd#oust_StereolabsAcquisitionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddc-78e1-a1d8-cc88c815c52e" xlink:to="loc_oust_StereolabsAcquisitionMember_019e8332-cddc-7a73-932d-61d309b87957" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_019e8332-cddc-7b19-b625-8b43781c6081" 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_019e8332-cddc-7e9f-8573-9e0f3fc68bd0" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_019e8332-cddc-7b19-b625-8b43781c6081" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019e8332-cddc-7b19-b625-8b43781c6081_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_019e8332-cddc-7b19-b625-8b43781c6081" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019e8332-cddc-7b19-b625-8b43781c6081_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019e8332-cddc-714c-adc5-6e29601b1bb1" 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_019e8332-cddc-7b19-b625-8b43781c6081" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019e8332-cddc-714c-adc5-6e29601b1bb1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_AmazonWarrantMember_019e8332-cddc-7f68-83bd-2e138c27ce06" xlink:href="oust-20260630.xsd#oust_AmazonWarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019e8332-cddc-714c-adc5-6e29601b1bb1" xlink:to="loc_oust_AmazonWarrantMember_019e8332-cddc-7f68-83bd-2e138c27ce06" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019e8332-cddc-744a-bff7-f08805d868dd" 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_019e8332-cddc-7e9f-8573-9e0f3fc68bd0" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019e8332-cddc-744a-bff7-f08805d868dd" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019e8332-cddc-744a-bff7-f08805d868dd_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_019e8332-cddc-744a-bff7-f08805d868dd" xlink:to="loc_us-gaap_EquityComponentDomain_019e8332-cddc-744a-bff7-f08805d868dd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019e8332-cddc-7afe-8cdd-3cd03611ee9c" 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_019e8332-cddc-744a-bff7-f08805d868dd" xlink:to="loc_us-gaap_EquityComponentDomain_019e8332-cddc-7afe-8cdd-3cd03611ee9c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019e8332-cddc-7e68-9658-7b4ecf70cc29" 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_019e8332-cddc-7afe-8cdd-3cd03611ee9c" xlink:to="loc_us-gaap_CommonStockMember_019e8332-cddc-7e68-9658-7b4ecf70cc29" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_019e8332-cddc-7bac-bc63-a1c017c0bc49" 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_ClassOfWarrantOrRightTable_019e8332-cddc-7e9f-8573-9e0f3fc68bd0" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_019e8332-cddc-7bac-bc63-a1c017c0bc49" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019e8332-cddc-7bac-bc63-a1c017c0bc49_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_019e8332-cddc-7bac-bc63-a1c017c0bc49" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019e8332-cddc-7bac-bc63-a1c017c0bc49_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019e8332-cddc-7fd2-81da-d238c22f55bd" 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_019e8332-cddc-7bac-bc63-a1c017c0bc49" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019e8332-cddc-7fd2-81da-d238c22f55bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputExpectedTermMember_019e8332-cddc-726c-a77c-6c58d7e64859" 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_019e8332-cddc-7fd2-81da-d238c22f55bd" xlink:to="loc_us-gaap_MeasurementInputExpectedTermMember_019e8332-cddc-726c-a77c-6c58d7e64859" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputPriceVolatilityMember_019e8332-cddc-768a-b877-567c4226eb6c" 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_019e8332-cddc-7fd2-81da-d238c22f55bd" xlink:to="loc_us-gaap_MeasurementInputPriceVolatilityMember_019e8332-cddc-768a-b877-567c4226eb6c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputRiskFreeInterestRateMember_019e8332-cddc-7653-9424-a1c6ba232a95" 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_019e8332-cddc-7fd2-81da-d238c22f55bd" xlink:to="loc_us-gaap_MeasurementInputRiskFreeInterestRateMember_019e8332-cddc-7653-9424-a1c6ba232a95" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputExpectedDividendRateMember_019e8332-cddc-7ba9-82cd-5a22eb36bc93" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputExpectedDividendRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019e8332-cddc-7fd2-81da-d238c22f55bd" xlink:to="loc_us-gaap_MeasurementInputExpectedDividendRateMember_019e8332-cddc-7ba9-82cd-5a22eb36bc93" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueAxis_019e8332-cddc-782e-8ab6-2430c7bb0932" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ValuationTechniqueAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfWarrantOrRightTable_019e8332-cddc-7e9f-8573-9e0f3fc68bd0" xlink:to="loc_us-gaap_ValuationTechniqueAxis_019e8332-cddc-782e-8ab6-2430c7bb0932" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_019e8332-cddc-782e-8ab6-2430c7bb0932_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ValuationTechniqueAxis_019e8332-cddc-782e-8ab6-2430c7bb0932" xlink:to="loc_us-gaap_ValuationTechniqueDomain_019e8332-cddc-782e-8ab6-2430c7bb0932_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_019e8332-cddc-7f18-9b91-0660499386eb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ValuationTechniqueAxis_019e8332-cddc-782e-8ab6-2430c7bb0932" xlink:to="loc_us-gaap_ValuationTechniqueDomain_019e8332-cddc-7f18-9b91-0660499386eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueOptionPricingModelMember_019e8332-cddc-796a-9e17-63f6f78e0aa5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ValuationTechniqueOptionPricingModelMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationTechniqueDomain_019e8332-cddc-7f18-9b91-0660499386eb" xlink:to="loc_us-gaap_ValuationTechniqueOptionPricingModelMember_019e8332-cddc-796a-9e17-63f6f78e0aa5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_019f22cc-0c08-7390-abad-98e9fb8d2ebe" 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_ClassOfWarrantOrRightTable_019e8332-cddc-7e9f-8573-9e0f3fc68bd0" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_019f22cc-0c08-7390-abad-98e9fb8d2ebe" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019f22cc-0c08-7390-abad-98e9fb8d2ebe_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_019f22cc-0c08-7390-abad-98e9fb8d2ebe" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019f22cc-0c08-7390-abad-98e9fb8d2ebe_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019f22cc-0c08-7656-bae4-9da27e9e039a" 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_019f22cc-0c08-7390-abad-98e9fb8d2ebe" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019f22cc-0c08-7656-bae4-9da27e9e039a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_AtMarketIssuanceSalesAgreement2025Member_019f22cc-1898-7a6e-b5a0-a0126e84a21d" xlink:href="oust-20260630.xsd#oust_AtMarketIssuanceSalesAgreement2025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019f22cc-0c08-7656-bae4-9da27e9e039a" xlink:to="loc_oust_AtMarketIssuanceSalesAgreement2025Member_019f22cc-1898-7a6e-b5a0-a0126e84a21d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019e8332-cddc-726e-9e70-9eefb0fa706a" 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_019e8332-cddc-729b-bd3c-4953aeef42ed" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019e8332-cddc-726e-9e70-9eefb0fa706a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019e8332-cddc-7323-8b1b-8b8cc624eb28" 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_019e8332-cddc-729b-bd3c-4953aeef42ed" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019e8332-cddc-7323-8b1b-8b8cc624eb28" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesAcquisitions_019e8332-cddc-788a-a12d-97fbc4101609" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesAcquisitions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019e8332-cddc-729b-bd3c-4953aeef42ed" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesAcquisitions_019e8332-cddc-788a-a12d-97fbc4101609" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_ClassOfWarrantOrRightAdditionalNumberOfSecuritiesCalledByWarrantsOrRights_019e8332-cddc-76d4-9a96-1ad744705188" xlink:href="oust-20260630.xsd#oust_ClassOfWarrantOrRightAdditionalNumberOfSecuritiesCalledByWarrantsOrRights"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019e8332-cddc-729b-bd3c-4953aeef42ed" xlink:to="loc_oust_ClassOfWarrantOrRightAdditionalNumberOfSecuritiesCalledByWarrantsOrRights_019e8332-cddc-76d4-9a96-1ad744705188" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_019f22cb-c349-7c07-8e90-00f115acc70b" 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_ClassOfWarrantOrRightLineItems_019e8332-cddc-729b-bd3c-4953aeef42ed" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_019f22cb-c349-7c07-8e90-00f115acc70b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_ClassOfWarrantOrRightVestingBasisPaymentsByCounterpartyForGoodsAndServicesMaximum_019e8332-cddc-7d07-857c-85d338ffcc06" xlink:href="oust-20260630.xsd#oust_ClassOfWarrantOrRightVestingBasisPaymentsByCounterpartyForGoodsAndServicesMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019e8332-cddc-729b-bd3c-4953aeef42ed" xlink:to="loc_oust_ClassOfWarrantOrRightVestingBasisPaymentsByCounterpartyForGoodsAndServicesMaximum_019e8332-cddc-7d07-857c-85d338ffcc06" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantsAndRightsOutstandingMeasurementInput_019e8332-cddc-756f-9cb0-7abf8ca38c86" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantsAndRightsOutstandingMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019e8332-cddc-729b-bd3c-4953aeef42ed" xlink:to="loc_us-gaap_WarrantsAndRightsOutstandingMeasurementInput_019e8332-cddc-756f-9cb0-7abf8ca38c86" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_ClassOfWarrantOrRightNumberOfWarrantsVestedDuringPeriod_019e8332-cddc-721c-b6b3-5432513425b6" xlink:href="oust-20260630.xsd#oust_ClassOfWarrantOrRightNumberOfWarrantsVestedDuringPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019e8332-cddc-729b-bd3c-4953aeef42ed" xlink:to="loc_oust_ClassOfWarrantOrRightNumberOfWarrantsVestedDuringPeriod_019e8332-cddc-721c-b6b3-5432513425b6" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_ClassOfWarrantOrRightNumberOfWarrantsVested_019e8332-cddc-71f6-abaf-648bde696b78" xlink:href="oust-20260630.xsd#oust_ClassOfWarrantOrRightNumberOfWarrantsVested"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019e8332-cddc-729b-bd3c-4953aeef42ed" xlink:to="loc_oust_ClassOfWarrantOrRightNumberOfWarrantsVested_019e8332-cddc-71f6-abaf-648bde696b78" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/CommitmentsandContingenciesDetails" xlink:type="simple" xlink:href="oust-20260630.xsd#CommitmentsandContingenciesDetails"/>
  <link:definitionLink xlink:role="http://ouster.com/role/CommitmentsandContingenciesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesLineItems_019e8332-cddc-7b04-97c7-7330ae79d74b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LossContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesTable_019e8332-cddc-7264-ad42-c72d54426549" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LossContingenciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_019e8332-cddc-7b04-97c7-7330ae79d74b" xlink:to="loc_us-gaap_LossContingenciesTable_019e8332-cddc-7264-ad42-c72d54426549" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019e8332-cddc-76ce-87d8-7e293f686524" 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_LossContingenciesTable_019e8332-cddc-7264-ad42-c72d54426549" xlink:to="loc_srt_CounterpartyNameAxis_019e8332-cddc-76ce-87d8-7e293f686524" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e8332-cddc-76ce-87d8-7e293f686524_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_019e8332-cddc-76ce-87d8-7e293f686524" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e8332-cddc-76ce-87d8-7e293f686524_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e8332-cddc-7b87-b70b-f7d9f616c307" 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_019e8332-cddc-76ce-87d8-7e293f686524" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e8332-cddc-7b87-b70b-f7d9f616c307" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_ThirdPartyContractManufacturerMember_019e8332-cddc-742b-8f1e-35c132010dc5" xlink:href="oust-20260630.xsd#oust_ThirdPartyContractManufacturerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e8332-cddc-7b87-b70b-f7d9f616c307" xlink:to="loc_oust_ThirdPartyContractManufacturerMember_019e8332-cddc-742b-8f1e-35c132010dc5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_OtherVendorsMember_019e8332-cddc-75d5-9ef9-665d9f50df44" xlink:href="oust-20260630.xsd#oust_OtherVendorsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e8332-cddc-7b87-b70b-f7d9f616c307" xlink:to="loc_oust_OtherVendorsMember_019e8332-cddc-75d5-9ef9-665d9f50df44" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_HesaiPhotonicsMember_019e8332-cddc-75b5-b249-ae479a71eebf" xlink:href="oust-20260630.xsd#oust_HesaiPhotonicsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e8332-cddc-7b87-b70b-f7d9f616c307" xlink:to="loc_oust_HesaiPhotonicsMember_019e8332-cddc-75b5-b249-ae479a71eebf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LettersOfCreditOutstandingAmount_019e8332-cddc-7dea-8d14-b3b7ab770761" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LettersOfCreditOutstandingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019e8332-cddc-7b04-97c7-7330ae79d74b" xlink:to="loc_us-gaap_LettersOfCreditOutstandingAmount_019e8332-cddc-7dea-8d14-b3b7ab770761" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrecordedUnconditionalPurchaseObligationBalanceSheetAmount_019e8332-cddc-7ae2-b1f9-0f689aa7413c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnrecordedUnconditionalPurchaseObligationBalanceSheetAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019e8332-cddc-7b04-97c7-7330ae79d74b" xlink:to="loc_us-gaap_UnrecordedUnconditionalPurchaseObligationBalanceSheetAmount_019e8332-cddc-7ae2-b1f9-0f689aa7413c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationSettlementAmountAwardedToOtherParty_019e8332-cddc-7a56-b902-98bbfff136ac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LitigationSettlementAmountAwardedToOtherParty"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019e8332-cddc-7b04-97c7-7330ae79d74b" xlink:to="loc_us-gaap_LitigationSettlementAmountAwardedToOtherParty_019e8332-cddc-7a56-b902-98bbfff136ac" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_LossContingenciesNumberOfPatentsUnderReview_019e8332-cddc-7149-87fe-9bbb7553074c" xlink:href="oust-20260630.xsd#oust_LossContingenciesNumberOfPatentsUnderReview"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019e8332-cddc-7b04-97c7-7330ae79d74b" xlink:to="loc_oust_LossContingenciesNumberOfPatentsUnderReview_019e8332-cddc-7149-87fe-9bbb7553074c" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/CommonStockDetails" xlink:type="simple" xlink:href="oust-20260630.xsd#CommonStockDetails"/>
  <link:definitionLink xlink:role="http://ouster.com/role/CommonStockDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_019f22d5-f58c-72e3-a552-791380a2febc" 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_019e8332-cddc-7bc5-acdc-d14097bc390b" 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_019f22d5-f58c-72e3-a552-791380a2febc" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_019e8332-cddc-7bc5-acdc-d14097bc390b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_019f22de-8f4b-7ec0-98ba-7014aa00a7ee" 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_019e8332-cddc-7bc5-acdc-d14097bc390b" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_019f22de-8f4b-7ec0-98ba-7014aa00a7ee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019f22de-8f4b-7ec0-98ba-7014aa00a7ee_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_019f22de-8f4b-7ec0-98ba-7014aa00a7ee" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019f22de-8f4b-7ec0-98ba-7014aa00a7ee_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019f22de-8f4b-792a-980a-1c27df112b9b" 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_019f22de-8f4b-7ec0-98ba-7014aa00a7ee" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019f22de-8f4b-792a-980a-1c27df112b9b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_AtMarketIssuanceSalesAgreement2025Member_019f22de-ad05-70da-a710-ac05073417a9" xlink:href="oust-20260630.xsd#oust_AtMarketIssuanceSalesAgreement2025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019f22de-8f4b-792a-980a-1c27df112b9b" xlink:to="loc_oust_AtMarketIssuanceSalesAgreement2025Member_019f22de-ad05-70da-a710-ac05073417a9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_AtMarketIssuanceSalesAgreement2026Member_019f4554-27c3-7d18-8120-9ac9ed8df77e" xlink:href="oust-20260630.xsd#oust_AtMarketIssuanceSalesAgreement2026Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019f22de-8f4b-792a-980a-1c27df112b9b" xlink:to="loc_oust_AtMarketIssuanceSalesAgreement2026Member_019f4554-27c3-7d18-8120-9ac9ed8df77e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_PublicOfferingMember_019f8fcc-bf80-7f30-927a-728045964695" xlink:href="oust-20260630.xsd#oust_PublicOfferingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019f22de-8f4b-792a-980a-1c27df112b9b" xlink:to="loc_oust_PublicOfferingMember_019f8fcc-bf80-7f30-927a-728045964695" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019f22df-1a9b-7969-b5d4-4fe8abda9e1e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019e8332-cddc-7bc5-acdc-d14097bc390b" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019f22df-1a9b-7969-b5d4-4fe8abda9e1e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019f22df-1a9b-7969-b5d4-4fe8abda9e1e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019f22df-1a9b-7969-b5d4-4fe8abda9e1e" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019f22df-1a9b-7969-b5d4-4fe8abda9e1e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019f22df-1a9b-791a-931f-bb298ba40025" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019f22df-1a9b-7969-b5d4-4fe8abda9e1e" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019f22df-1a9b-791a-931f-bb298ba40025" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_StereoLabsMember_019f22df-1a9b-7076-80c1-ca24142fb4f0" xlink:href="oust-20260630.xsd#oust_StereoLabsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019f22df-1a9b-791a-931f-bb298ba40025" xlink:to="loc_oust_StereoLabsMember_019f22df-1a9b-7076-80c1-ca24142fb4f0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityInterestIssuedOrIssuableByTypeAxis_019f22df-1a9b-73b0-9751-bc5a4d602946" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityInterestIssuedOrIssuableByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019e8332-cddc-7bc5-acdc-d14097bc390b" xlink:to="loc_us-gaap_EquityInterestIssuedOrIssuableByTypeAxis_019f22df-1a9b-73b0-9751-bc5a4d602946" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityInterestIssuedOrIssuableTypeDomain_019f22df-1a9b-73b0-9751-bc5a4d602946_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityInterestIssuedOrIssuableTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_EquityInterestIssuedOrIssuableByTypeAxis_019f22df-1a9b-73b0-9751-bc5a4d602946" xlink:to="loc_us-gaap_EquityInterestIssuedOrIssuableTypeDomain_019f22df-1a9b-73b0-9751-bc5a4d602946_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityInterestIssuedOrIssuableTypeDomain_019f22df-1a9b-7587-a40d-a64a239c3fbb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityInterestIssuedOrIssuableTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_EquityInterestIssuedOrIssuableByTypeAxis_019f22df-1a9b-73b0-9751-bc5a4d602946" xlink:to="loc_us-gaap_EquityInterestIssuedOrIssuableTypeDomain_019f22df-1a9b-7587-a40d-a64a239c3fbb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019f22df-1a9b-7737-a9cd-4c8fa2f3a41a" 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_EquityInterestIssuedOrIssuableTypeDomain_019f22df-1a9b-7587-a40d-a64a239c3fbb" xlink:to="loc_us-gaap_CommonStockMember_019f22df-1a9b-7737-a9cd-4c8fa2f3a41a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_019f8fcc-bf80-7b7e-85ff-3be21694abcb" 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_ScheduleOfStockByClassTable_019e8332-cddc-7bc5-acdc-d14097bc390b" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_019f8fcc-bf80-7b7e-85ff-3be21694abcb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019f8fcc-bf80-7b7e-85ff-3be21694abcb_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_019f8fcc-bf80-7b7e-85ff-3be21694abcb" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019f8fcc-bf80-7b7e-85ff-3be21694abcb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019f8fcc-bf80-7b5c-bccb-09acbd0a0248" 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_019f8fcc-bf80-7b7e-85ff-3be21694abcb" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019f8fcc-bf80-7b5c-bccb-09acbd0a0248" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_019f8fcc-bf80-79d8-9bcf-f92d5b3022d2" 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_019f8fcc-bf80-7b5c-bccb-09acbd0a0248" xlink:to="loc_us-gaap_SubsequentEventMember_019f8fcc-bf80-79d8-9bcf-f92d5b3022d2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_019f22d5-f58c-7a12-809b-ff9997f5be20" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019f22d5-f58c-72e3-a552-791380a2febc" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_019f22d5-f58c-7a12-809b-ff9997f5be20" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockParOrStatedValuePerShare_019f22d5-f58c-723b-8450-7f53967a3fba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019f22d5-f58c-72e3-a552-791380a2febc" xlink:to="loc_us-gaap_PreferredStockParOrStatedValuePerShare_019f22d5-f58c-723b-8450-7f53967a3fba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_019f22d5-f58c-7446-b812-e6e70a81231c" 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_ClassOfStockLineItems_019f22d5-f58c-72e3-a552-791380a2febc" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_019f22d5-f58c-7446-b812-e6e70a81231c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_019f22d5-f58c-7f48-b409-54b65b57f312" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019f22d5-f58c-72e3-a552-791380a2febc" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_019f22d5-f58c-7f48-b409-54b65b57f312" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_CommonStockVotingRightsNumberOfVotesForEachShareHeld_019f22d5-f58c-76a4-a2eb-1eabf568edac" xlink:href="oust-20260630.xsd#oust_CommonStockVotingRightsNumberOfVotesForEachShareHeld"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019f22d5-f58c-72e3-a552-791380a2febc" xlink:to="loc_oust_CommonStockVotingRightsNumberOfVotesForEachShareHeld_019f22d5-f58c-76a4-a2eb-1eabf568edac" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_SaleOfStockAuthorizedAmount_019f22de-8f4b-75ca-8017-cb3d6bae2911" xlink:href="oust-20260630.xsd#oust_SaleOfStockAuthorizedAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019f22d5-f58c-72e3-a552-791380a2febc" xlink:to="loc_oust_SaleOfStockAuthorizedAmount_019f22de-8f4b-75ca-8017-cb3d6bae2911" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_019f22de-ad05-78f6-98e1-80a62682935a" 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_019f22d5-f58c-72e3-a552-791380a2febc" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_019f22de-ad05-78f6-98e1-80a62682935a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_SaleOfStockWeightedAverageStockPricePerShare_019f22de-ad05-7840-b8b7-4816839884a4" xlink:href="oust-20260630.xsd#oust_SaleOfStockWeightedAverageStockPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019f22d5-f58c-72e3-a552-791380a2febc" xlink:to="loc_oust_SaleOfStockWeightedAverageStockPricePerShare_019f22de-ad05-7840-b8b7-4816839884a4" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_019f22de-ad05-730f-b73f-0258cf0a85ce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019f22d5-f58c-72e3-a552-791380a2febc" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_019f22de-ad05-730f-b73f-0258cf0a85ce" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_ProceedsFromIssuanceOfCommonStockNetOfIssuanceCosts_019f22de-ad05-7784-bddf-3c774805c3aa" xlink:href="oust-20260630.xsd#oust_ProceedsFromIssuanceOfCommonStockNetOfIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019f22d5-f58c-72e3-a552-791380a2febc" xlink:to="loc_oust_ProceedsFromIssuanceOfCommonStockNetOfIssuanceCosts_019f22de-ad05-7784-bddf-3c774805c3aa" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_019f22df-1a9b-710f-ae75-d0ed7b7c9ea3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019f22d5-f58c-72e3-a552-791380a2febc" xlink:to="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_019f22df-1a9b-710f-ae75-d0ed7b7c9ea3" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_BusinessCombinationConsiderationTransferredEquityInterestIssuedAndIssuableSharesSubjectToLockUpArrangement_019f22df-1a9b-70a8-b96e-3a2f6a96feef" xlink:href="oust-20260630.xsd#oust_BusinessCombinationConsiderationTransferredEquityInterestIssuedAndIssuableSharesSubjectToLockUpArrangement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019f22d5-f58c-72e3-a552-791380a2febc" xlink:to="loc_oust_BusinessCombinationConsiderationTransferredEquityInterestIssuedAndIssuableSharesSubjectToLockUpArrangement_019f22df-1a9b-70a8-b96e-3a2f6a96feef" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_BusinessCombinationStaggeredLockUpArrangementForSharesServicePeriod_019f22df-1a9b-7f2c-a9bc-86bfbda66cb8" xlink:href="oust-20260630.xsd#oust_BusinessCombinationStaggeredLockUpArrangementForSharesServicePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019f22d5-f58c-72e3-a552-791380a2febc" xlink:to="loc_oust_BusinessCombinationStaggeredLockUpArrangementForSharesServicePeriod_019f22df-1a9b-7f2c-a9bc-86bfbda66cb8" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019f8fcc-bf80-7fa4-8efe-2785372761e7" 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_ClassOfStockLineItems_019f22d5-f58c-72e3-a552-791380a2febc" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019f8fcc-bf80-7fa4-8efe-2785372761e7" xlink:type="arc" order="13"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/StockbasedCompensationNarrativeDetails" xlink:type="simple" xlink:href="oust-20260630.xsd#StockbasedCompensationNarrativeDetails"/>
  <link:definitionLink xlink:role="http://ouster.com/role/StockbasedCompensationNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8332-cddc-7ca1-8a5b-b4f27452fd48" 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_019e8332-cddc-7a0e-bdae-1c0f226b9d9f" 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_019e8332-cddc-7ca1-8a5b-b4f27452fd48" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e8332-cddc-7a0e-bdae-1c0f226b9d9f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019e8332-cddc-7663-9f59-00ebd8d49366" 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_019e8332-cddc-7a0e-bdae-1c0f226b9d9f" xlink:to="loc_us-gaap_AwardTypeAxis_019e8332-cddc-7663-9f59-00ebd8d49366" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e8332-cddc-7663-9f59-00ebd8d49366_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_019e8332-cddc-7663-9f59-00ebd8d49366" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e8332-cddc-7663-9f59-00ebd8d49366_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e8332-cddc-7b02-9d85-cf4b9e56c5a6" 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_019e8332-cddc-7663-9f59-00ebd8d49366" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e8332-cddc-7b02-9d85-cf4b9e56c5a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019e8332-cddc-7f18-bc18-9304b8244eb1" 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_019e8332-cddc-7b02-9d85-cf4b9e56c5a6" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019e8332-cddc-7f18-bc18-9304b8244eb1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_019e8332-cddc-7d4a-9c9c-88fc3a33fb5b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e8332-cddc-7b02-9d85-cf4b9e56c5a6" xlink:to="loc_us-gaap_RestrictedStockMember_019e8332-cddc-7d4a-9c9c-88fc3a33fb5b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_019e8332-cddc-795a-882a-b2845a6d1d47" 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_019e8332-cddc-7a0e-bdae-1c0f226b9d9f" xlink:to="loc_us-gaap_PlanNameAxis_019e8332-cddc-795a-882a-b2845a6d1d47" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019e8332-cddc-795a-882a-b2845a6d1d47_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_019e8332-cddc-795a-882a-b2845a6d1d47" xlink:to="loc_us-gaap_PlanNameDomain_019e8332-cddc-795a-882a-b2845a6d1d47_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019e8332-cddc-7a85-84e7-1d4abb06afa4" 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_019e8332-cddc-795a-882a-b2845a6d1d47" xlink:to="loc_us-gaap_PlanNameDomain_019e8332-cddc-7a85-84e7-1d4abb06afa4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_A2022EmployeeStockPurchasePlanMember_019e8332-cddc-7d00-91e1-c0399a38aae2" xlink:href="oust-20260630.xsd#oust_A2022EmployeeStockPurchasePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019e8332-cddc-7a85-84e7-1d4abb06afa4" xlink:to="loc_oust_A2022EmployeeStockPurchasePlanMember_019e8332-cddc-7d00-91e1-c0399a38aae2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddc-745f-8ef0-ab27cb8b5443" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e8332-cddc-7a0e-bdae-1c0f226b9d9f" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddc-745f-8ef0-ab27cb8b5443" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddc-745f-8ef0-ab27cb8b5443_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddc-745f-8ef0-ab27cb8b5443" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddc-745f-8ef0-ab27cb8b5443_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddc-7696-a198-673ee2b8a559" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019e8332-cddc-745f-8ef0-ab27cb8b5443" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddc-7696-a198-673ee2b8a559" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_StereoLabsMember_019e8332-cddc-7c0d-9771-0828ff4fb36d" xlink:href="oust-20260630.xsd#oust_StereoLabsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e8332-cddc-7696-a198-673ee2b8a559" xlink:to="loc_oust_StereoLabsMember_019e8332-cddc-7c0d-9771-0828ff4fb36d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityInterestIssuedOrIssuableByTypeAxis_019e8332-cddc-71d1-9309-652c6a5a25d1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityInterestIssuedOrIssuableByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e8332-cddc-7a0e-bdae-1c0f226b9d9f" xlink:to="loc_us-gaap_EquityInterestIssuedOrIssuableByTypeAxis_019e8332-cddc-71d1-9309-652c6a5a25d1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityInterestIssuedOrIssuableTypeDomain_019e8332-cddc-71d1-9309-652c6a5a25d1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityInterestIssuedOrIssuableTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_EquityInterestIssuedOrIssuableByTypeAxis_019e8332-cddc-71d1-9309-652c6a5a25d1" xlink:to="loc_us-gaap_EquityInterestIssuedOrIssuableTypeDomain_019e8332-cddc-71d1-9309-652c6a5a25d1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityInterestIssuedOrIssuableTypeDomain_019e8332-cddc-7a9d-b19c-9411e68d29dd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityInterestIssuedOrIssuableTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_EquityInterestIssuedOrIssuableByTypeAxis_019e8332-cddc-71d1-9309-652c6a5a25d1" xlink:to="loc_us-gaap_EquityInterestIssuedOrIssuableTypeDomain_019e8332-cddc-7a9d-b19c-9411e68d29dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019e8332-cddc-787a-92e2-da3f1ca994ea" 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_EquityInterestIssuedOrIssuableTypeDomain_019e8332-cddc-7a9d-b19c-9411e68d29dd" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019e8332-cddc-787a-92e2-da3f1ca994ea" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019f67fc-34b7-71b5-8691-1883834103c9" 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_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e8332-cddc-7a0e-bdae-1c0f226b9d9f" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019f67fc-34b7-71b5-8691-1883834103c9" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019f67fc-34b7-71b5-8691-1883834103c9_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_019f67fc-34b7-71b5-8691-1883834103c9" xlink:to="loc_us-gaap_EquityComponentDomain_019f67fc-34b7-71b5-8691-1883834103c9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019f67fc-34b7-7e42-9783-575acdce3f07" 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_019f67fc-34b7-71b5-8691-1883834103c9" xlink:to="loc_us-gaap_EquityComponentDomain_019f67fc-34b7-7e42-9783-575acdce3f07" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019f67fc-34b7-729f-b09b-e59d0fda03fa" 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_019f67fc-34b7-7e42-9783-575acdce3f07" xlink:to="loc_us-gaap_CommonStockMember_019f67fc-34b7-729f-b09b-e59d0fda03fa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_019fb98d-ad86-72a8-ac4e-6c3ff277d9e2" 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_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e8332-cddc-7a0e-bdae-1c0f226b9d9f" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_019fb98d-ad86-72a8-ac4e-6c3ff277d9e2" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019fb98d-ad86-72a8-ac4e-6c3ff277d9e2_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_019fb98d-ad86-72a8-ac4e-6c3ff277d9e2" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019fb98d-ad86-72a8-ac4e-6c3ff277d9e2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019fb98d-ad86-712c-8884-741afbac078b" 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_019fb98d-ad86-72a8-ac4e-6c3ff277d9e2" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019fb98d-ad86-712c-8884-741afbac078b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_StereolabsWarrantsVestedMember_019fb98f-7a59-7480-b299-4e77c6a7da65" xlink:href="oust-20260630.xsd#oust_StereolabsWarrantsVestedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019fb98d-ad86-712c-8884-741afbac078b" xlink:to="loc_oust_StereolabsWarrantsVestedMember_019fb98f-7a59-7480-b299-4e77c6a7da65" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_ShareBasedPaymentArrangementNumberOfEquityIncentivePlans_019e8332-cddc-7cba-8d82-186a34e71a18" xlink:href="oust-20260630.xsd#oust_ShareBasedPaymentArrangementNumberOfEquityIncentivePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8332-cddc-7ca1-8a5b-b4f27452fd48" xlink:to="loc_oust_ShareBasedPaymentArrangementNumberOfEquityIncentivePlans_019e8332-cddc-7cba-8d82-186a34e71a18" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeSubscriptionRate_019e8332-cddc-7990-82ee-5c8f2d7f0891" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeSubscriptionRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8332-cddc-7ca1-8a5b-b4f27452fd48" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeSubscriptionRate_019e8332-cddc-7990-82ee-5c8f2d7f0891" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_EmployeeStockPurchasePlanOfferingPeriod_019e8332-cddc-70dd-9e64-7a2fa6b600de" xlink:href="oust-20260630.xsd#oust_EmployeeStockPurchasePlanOfferingPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8332-cddc-7ca1-8a5b-b4f27452fd48" xlink:to="loc_oust_EmployeeStockPurchasePlanOfferingPeriod_019e8332-cddc-70dd-9e64-7a2fa6b600de" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_ShareBasedCompensationArrangementByShareBasedPaymentAwardPurchasePeriod_019e8332-cddc-766b-8bec-8a0656699a30" xlink:href="oust-20260630.xsd#oust_ShareBasedCompensationArrangementByShareBasedPaymentAwardPurchasePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8332-cddc-7ca1-8a5b-b4f27452fd48" xlink:to="loc_oust_ShareBasedCompensationArrangementByShareBasedPaymentAwardPurchasePeriod_019e8332-cddc-766b-8bec-8a0656699a30" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_019e8332-cddc-7205-9586-9bbe402f7c84" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8332-cddc-7ca1-8a5b-b4f27452fd48" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_019e8332-cddc-7205-9586-9bbe402f7c84" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_019e8332-cddc-78c4-9b64-bbd07c356d76" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8332-cddc-7ca1-8a5b-b4f27452fd48" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_019e8332-cddc-78c4-9b64-bbd07c356d76" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_019e8332-cddc-731b-94e5-22f91819e025" 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_019e8332-cddc-7ca1-8a5b-b4f27452fd48" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_019e8332-cddc-731b-94e5-22f91819e025" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_019e8332-cddc-7e28-ae27-834e65faff13" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8332-cddc-7ca1-8a5b-b4f27452fd48" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_019e8332-cddc-7e28-ae27-834e65faff13" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019e8332-cddc-7fe7-ab80-ae1e8411d6f5" 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_019e8332-cddc-7ca1-8a5b-b4f27452fd48" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019e8332-cddc-7fe7-ab80-ae1e8411d6f5" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_BusinessCombinationConsiderationTransferredEquityInterestIssuedAndIssuableSharesSubjectToLockUpArrangement_019e8332-cddc-72c9-8e31-86fd82d97361" xlink:href="oust-20260630.xsd#oust_BusinessCombinationConsiderationTransferredEquityInterestIssuedAndIssuableSharesSubjectToLockUpArrangement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8332-cddc-7ca1-8a5b-b4f27452fd48" xlink:to="loc_oust_BusinessCombinationConsiderationTransferredEquityInterestIssuedAndIssuableSharesSubjectToLockUpArrangement_019e8332-cddc-72c9-8e31-86fd82d97361" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_BusinessCombinationStaggeredLockUpArrangementForSharesServicePeriod_019e8332-cddc-73ce-b2bc-505a0dea00e6" xlink:href="oust-20260630.xsd#oust_BusinessCombinationStaggeredLockUpArrangementForSharesServicePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8332-cddc-7ca1-8a5b-b4f27452fd48" xlink:to="loc_oust_BusinessCombinationStaggeredLockUpArrangementForSharesServicePeriod_019e8332-cddc-73ce-b2bc-505a0dea00e6" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_BusinessCombinationStaggeredLockUpArrangementSharesVestingPercent_019e8332-cddc-7f6d-a34d-64bd93ed8881" xlink:href="oust-20260630.xsd#oust_BusinessCombinationStaggeredLockUpArrangementSharesVestingPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8332-cddc-7ca1-8a5b-b4f27452fd48" xlink:to="loc_oust_BusinessCombinationStaggeredLockUpArrangementSharesVestingPercent_019e8332-cddc-7f6d-a34d-64bd93ed8881" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019e8332-cddc-7d00-9bf1-cb896ce6b7a1" 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_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8332-cddc-7ca1-8a5b-b4f27452fd48" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019e8332-cddc-7d00-9bf1-cb896ce6b7a1" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019e8332-cddc-7d74-b4b3-3df4756c900e" 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_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8332-cddc-7ca1-8a5b-b4f27452fd48" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019e8332-cddc-7d74-b4b3-3df4756c900e" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_019e8332-cddc-709b-9d05-c5150861224d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8332-cddc-7ca1-8a5b-b4f27452fd48" xlink:to="loc_us-gaap_ShareBasedCompensation_019e8332-cddc-709b-9d05-c5150861224d" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_019e8332-cddc-7d62-8b31-459ad3c563e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8332-cddc-7ca1-8a5b-b4f27452fd48" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_019e8332-cddc-7d62-8b31-459ad3c563e0" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss_019fa8ac-9e37-77f0-8d70-b3b225bb8b33" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8332-cddc-7ca1-8a5b-b4f27452fd48" xlink:to="loc_us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss_019fa8ac-9e37-77f0-8d70-b3b225bb8b33" xlink:type="arc" order="16"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/StockbasedCompensationScheduleofStockOptionsOutstandingandExercisableDetails" xlink:type="simple" xlink:href="oust-20260630.xsd#StockbasedCompensationScheduleofStockOptionsOutstandingandExercisableDetails"/>
  <link:definitionLink xlink:role="http://ouster.com/role/StockbasedCompensationScheduleofStockOptionsOutstandingandExercisableDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_019e8332-cddc-7a38-b5ea-47a819c25092" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeTable_019e8332-cddc-7c72-9a7b-bf93ea384f4b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_019e8332-cddc-7a38-b5ea-47a819c25092" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeTable_019e8332-cddc-7c72-9a7b-bf93ea384f4b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis_019e8332-cddc-774e-b6a1-8519e8242aad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeTable_019e8332-cddc-7c72-9a7b-bf93ea384f4b" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis_019e8332-cddc-774e-b6a1-8519e8242aad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_019e8332-cddc-774e-b6a1-8519e8242aad_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis_019e8332-cddc-774e-b6a1-8519e8242aad" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_019e8332-cddc-774e-b6a1-8519e8242aad_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_019e8332-cddc-7f52-bcc7-c5c53e209f90" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis_019e8332-cddc-774e-b6a1-8519e8242aad" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_019e8332-cddc-7f52-bcc7-c5c53e209f90" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_ExercisePriceRangeOneMember_019e8332-cddc-7b2f-a996-4313f5b9a673" xlink:href="oust-20260630.xsd#oust_ExercisePriceRangeOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_019e8332-cddc-7f52-bcc7-c5c53e209f90" xlink:to="loc_oust_ExercisePriceRangeOneMember_019e8332-cddc-7b2f-a996-4313f5b9a673" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_ExercisePriceRangeTwoMember_019e8332-cddc-791c-9275-5d9cc4f5d287" xlink:href="oust-20260630.xsd#oust_ExercisePriceRangeTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_019e8332-cddc-7f52-bcc7-c5c53e209f90" xlink:to="loc_oust_ExercisePriceRangeTwoMember_019e8332-cddc-791c-9275-5d9cc4f5d287" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_ExercisePriceRangeThreeMember_019e8332-cddc-719f-9c97-971f1720b1bf" xlink:href="oust-20260630.xsd#oust_ExercisePriceRangeThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_019e8332-cddc-7f52-bcc7-c5c53e209f90" xlink:to="loc_oust_ExercisePriceRangeThreeMember_019e8332-cddc-719f-9c97-971f1720b1bf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_ExercisePriceRangeFourMember_019e8332-cddc-7708-a982-4bfa581819e5" xlink:href="oust-20260630.xsd#oust_ExercisePriceRangeFourMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_019e8332-cddc-7f52-bcc7-c5c53e209f90" xlink:to="loc_oust_ExercisePriceRangeFourMember_019e8332-cddc-7708-a982-4bfa581819e5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit_019e8332-cddc-7ff8-9348-70a7b449d509" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_019e8332-cddc-7a38-b5ea-47a819c25092" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit_019e8332-cddc-7ff8-9348-70a7b449d509" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit_019e8332-cddc-7e20-aa9f-960654b51370" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_019e8332-cddc-7a38-b5ea-47a819c25092" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit_019e8332-cddc-7e20-aa9f-960654b51370" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions_019e8332-cddc-799a-9382-55655e72a40d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_019e8332-cddc-7a38-b5ea-47a819c25092" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions_019e8332-cddc-799a-9382-55655e72a40d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageRemainingContractualTerm2_019e8332-cddc-752c-a397-e87413d37175" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageRemainingContractualTerm2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_019e8332-cddc-7a38-b5ea-47a819c25092" xlink:to="loc_us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageRemainingContractualTerm2_019e8332-cddc-752c-a397-e87413d37175" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfExercisableOptions_019e8332-cddc-7b6c-a39a-8ac12c33ffc3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfExercisableOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_019e8332-cddc-7a38-b5ea-47a819c25092" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfExercisableOptions_019e8332-cddc-7b6c-a39a-8ac12c33ffc3" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/StockbasedCompensationScheduleofRestrictedStockUnitsActivityDetails" xlink:type="simple" xlink:href="oust-20260630.xsd#StockbasedCompensationScheduleofRestrictedStockUnitsActivityDetails"/>
  <link:definitionLink xlink:role="http://ouster.com/role/StockbasedCompensationScheduleofRestrictedStockUnitsActivityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8332-cddc-7f16-a083-b3473b5eb4c1" 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_019e8332-cddc-7837-9c70-fb4a5adfadfe" 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_019e8332-cddc-7f16-a083-b3473b5eb4c1" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e8332-cddc-7837-9c70-fb4a5adfadfe" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019e8332-cddc-7988-afe6-09753fb4e2f8" 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_019e8332-cddc-7837-9c70-fb4a5adfadfe" xlink:to="loc_us-gaap_AwardTypeAxis_019e8332-cddc-7988-afe6-09753fb4e2f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e8332-cddc-7988-afe6-09753fb4e2f8_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_019e8332-cddc-7988-afe6-09753fb4e2f8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e8332-cddc-7988-afe6-09753fb4e2f8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e8332-cddc-7ed4-9bac-a0197619d55e" 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_019e8332-cddc-7988-afe6-09753fb4e2f8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e8332-cddc-7ed4-9bac-a0197619d55e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019e8332-cddc-7470-a63f-dd179c89933d" 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_019e8332-cddc-7ed4-9bac-a0197619d55e" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019e8332-cddc-7470-a63f-dd179c89933d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019e8332-cddc-7f87-8f02-668014d4941e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8332-cddc-7f16-a083-b3473b5eb4c1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019e8332-cddc-7f87-8f02-668014d4941e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019e8332-cddc-7b39-9579-0ce046d2aad6" 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_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019e8332-cddc-7f87-8f02-668014d4941e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019e8332-cddc-7b39-9579-0ce046d2aad6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019e8332-cddc-7c88-9190-db9091b34422" 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_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019e8332-cddc-7f87-8f02-668014d4941e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019e8332-cddc-7c88-9190-db9091b34422" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsCanceledInPeriod_019e8332-cddc-71ec-a9d9-880e4aedf635" xlink:href="oust-20260630.xsd#oust_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsCanceledInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019e8332-cddc-7f87-8f02-668014d4941e" xlink:to="loc_oust_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsCanceledInPeriod_019e8332-cddc-71ec-a9d9-880e4aedf635" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019e8332-cddc-7a3f-940a-564b4a248962" 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_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019e8332-cddc-7f87-8f02-668014d4941e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019e8332-cddc-7a3f-940a-564b4a248962" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019e8332-cddc-7899-ba9c-70808e6f84e7" 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_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019e8332-cddc-728a-8a34-292fd643b0ed" 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_019e8332-cddc-7f16-a083-b3473b5eb4c1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019e8332-cddc-728a-8a34-292fd643b0ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019e8332-cddc-7684-ae2b-99ce90c4795d" 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_019e8332-cddc-728a-8a34-292fd643b0ed" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019e8332-cddc-7684-ae2b-99ce90c4795d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019e8332-cddc-7218-a23b-a61913a9054d" 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_019e8332-cddc-728a-8a34-292fd643b0ed" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019e8332-cddc-7218-a23b-a61913a9054d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsCancellationsWeightedAverageGrantDateFairValue_019e8332-cddc-79f6-82cf-527132c72961" xlink:href="oust-20260630.xsd#oust_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsCancellationsWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019e8332-cddc-728a-8a34-292fd643b0ed" xlink:to="loc_oust_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsCancellationsWeightedAverageGrantDateFairValue_019e8332-cddc-79f6-82cf-527132c72961" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_019e8332-cddc-79e0-80c1-c64a244731bf" 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_019e8332-cddc-728a-8a34-292fd643b0ed" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_019e8332-cddc-79e0-80c1-c64a244731bf" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019e8332-cddc-778b-87d5-07dfb356d0df" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/StockbasedCompensationScheduleofStockbasedCompensationDetails" xlink:type="simple" xlink:href="oust-20260630.xsd#StockbasedCompensationScheduleofStockbasedCompensationDetails"/>
  <link:definitionLink xlink:role="http://ouster.com/role/StockbasedCompensationScheduleofStockbasedCompensationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e8332-cddc-7390-8536-b76a72de62f5" 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_019e8332-cddc-71e0-abda-7c6348790b1f" 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_019e8332-cddc-7390-8536-b76a72de62f5" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019e8332-cddc-71e0-abda-7c6348790b1f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019e8332-cddc-7f51-b0e6-ace1fa8aa9b4" 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_019e8332-cddc-71e0-abda-7c6348790b1f" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019e8332-cddc-7f51-b0e6-ace1fa8aa9b4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019e8332-cddc-76fa-b81a-5c733e3023bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e8332-cddc-7390-8536-b76a72de62f5" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019e8332-cddc-76fa-b81a-5c733e3023bf" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/StockbasedCompensationScheduleofStockbasedCompensationDetails_1" xlink:type="simple" xlink:href="oust-20260630.xsd#StockbasedCompensationScheduleofStockbasedCompensationDetails_1"/>
  <link:definitionLink xlink:role="http://ouster.com/role/StockbasedCompensationScheduleofStockbasedCompensationDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e8332-cddc-7390-8536-b76a72de62f5" 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_019e8332-cddc-71e0-abda-7c6348790b1f" 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_019e8332-cddc-7390-8536-b76a72de62f5" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019e8332-cddc-71e0-abda-7c6348790b1f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019e8332-cddc-76fa-b81a-5c733e3023bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e8332-cddc-7390-8536-b76a72de62f5" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019e8332-cddc-76fa-b81a-5c733e3023bf" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/StockbasedCompensationScheduleofStockCompensationExpensebyAwardTypeDetails" xlink:type="simple" xlink:href="oust-20260630.xsd#StockbasedCompensationScheduleofStockCompensationExpensebyAwardTypeDetails"/>
  <link:definitionLink xlink:role="http://ouster.com/role/StockbasedCompensationScheduleofStockCompensationExpensebyAwardTypeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8332-cddc-7ec7-8a3e-a4c93199a83e" 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_019e8332-cddc-795c-b0b6-06bef8115085" 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_019e8332-cddc-7ec7-8a3e-a4c93199a83e" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e8332-cddc-795c-b0b6-06bef8115085" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019e8332-cddc-7504-99cf-c1c7c459811b" 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_019e8332-cddc-795c-b0b6-06bef8115085" xlink:to="loc_us-gaap_AwardTypeAxis_019e8332-cddc-7504-99cf-c1c7c459811b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e8332-cddc-7504-99cf-c1c7c459811b_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_019e8332-cddc-7504-99cf-c1c7c459811b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e8332-cddc-7504-99cf-c1c7c459811b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e8332-cddc-7413-98f3-34f8266d7338" 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_019e8332-cddc-7504-99cf-c1c7c459811b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e8332-cddc-7413-98f3-34f8266d7338" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019e8332-cddc-7834-8edf-37cea37e2f93" 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_019e8332-cddc-7413-98f3-34f8266d7338" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019e8332-cddc-7834-8edf-37cea37e2f93" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_019e8332-cddc-7c65-9c22-cd74ca040f99" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e8332-cddc-7413-98f3-34f8266d7338" xlink:to="loc_us-gaap_EmployeeStockMember_019e8332-cddc-7c65-9c22-cd74ca040f99" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_019e8332-cddc-73f4-8aed-6b188ed6e638" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e8332-cddc-7413-98f3-34f8266d7338" xlink:to="loc_us-gaap_RestrictedStockMember_019e8332-cddc-73f4-8aed-6b188ed6e638" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_StereolabsPostCombinationCompensationExpenseMember_019e8332-cddc-74b6-a17e-294866c2deac" xlink:href="oust-20260630.xsd#oust_StereolabsPostCombinationCompensationExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e8332-cddc-7413-98f3-34f8266d7338" xlink:to="loc_oust_StereolabsPostCombinationCompensationExpenseMember_019e8332-cddc-74b6-a17e-294866c2deac" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019e8332-cddc-793b-979a-2644e67889e7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8332-cddc-7ec7-8a3e-a4c93199a83e" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019e8332-cddc-793b-979a-2644e67889e7" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/NetLossPerCommonShareScheduleofAntidilutiveSecuritiesExcludedfromComputationofNetLossPerCommonShareDetails" xlink:type="simple" xlink:href="oust-20260630.xsd#NetLossPerCommonShareScheduleofAntidilutiveSecuritiesExcludedfromComputationofNetLossPerCommonShareDetails"/>
  <link:definitionLink xlink:role="http://ouster.com/role/NetLossPerCommonShareScheduleofAntidilutiveSecuritiesExcludedfromComputationofNetLossPerCommonShareDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019e8332-cddc-7dbe-95c2-77901f296950" 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_019e8332-cddc-7c2f-a856-e7e2cc546e85" 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_019e8332-cddc-7dbe-95c2-77901f296950" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019e8332-cddc-7c2f-a856-e7e2cc546e85" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019e8332-cddc-78c9-a8f7-f2f9586c736d" 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_019e8332-cddc-7c2f-a856-e7e2cc546e85" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019e8332-cddc-78c9-a8f7-f2f9586c736d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e8332-cddc-78c9-a8f7-f2f9586c736d_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_019e8332-cddc-78c9-a8f7-f2f9586c736d" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e8332-cddc-78c9-a8f7-f2f9586c736d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e8332-cddc-705a-8ae8-5d38d04d3141" 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_019e8332-cddc-78c9-a8f7-f2f9586c736d" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e8332-cddc-705a-8ae8-5d38d04d3141" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOptionsToPurchaseCommonStockMember_019e8332-cddc-77ac-91a8-7a7f58ac8c78" xlink:href="oust-20260630.xsd#oust_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOptionsToPurchaseCommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e8332-cddc-705a-8ae8-5d38d04d3141" xlink:to="loc_oust_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOptionsToPurchaseCommonStockMember_019e8332-cddc-77ac-91a8-7a7f58ac8c78" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_PublicAndPrivateCommonStockWarrantsMember_019e8332-cddc-7538-b729-d006f68652dc" xlink:href="oust-20260630.xsd#oust_PublicAndPrivateCommonStockWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e8332-cddc-705a-8ae8-5d38d04d3141" xlink:to="loc_oust_PublicAndPrivateCommonStockWarrantsMember_019e8332-cddc-7538-b729-d006f68652dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019e8332-cddc-78ab-9745-94a6a0117016" 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_AntidilutiveSecuritiesNameDomain_019e8332-cddc-705a-8ae8-5d38d04d3141" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019e8332-cddc-78ab-9745-94a6a0117016" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_BusinessCombinationRestrictStockUnitsIssuedMember_019e8332-cddc-7b43-80ba-33118595f624" xlink:href="oust-20260630.xsd#oust_BusinessCombinationRestrictStockUnitsIssuedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e8332-cddc-705a-8ae8-5d38d04d3141" xlink:to="loc_oust_BusinessCombinationRestrictStockUnitsIssuedMember_019e8332-cddc-7b43-80ba-33118595f624" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_019e8332-cddc-79ea-8455-681fa3b9a00c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e8332-cddc-705a-8ae8-5d38d04d3141" xlink:to="loc_us-gaap_EmployeeStockMember_019e8332-cddc-79ea-8455-681fa3b9a00c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_ShareBasedCompensationArrangementByShareBasedPaymentAwardUnvestedRestrictedStockAwardMember_019e8332-cddc-769f-a67d-149dbb2f5deb" xlink:href="oust-20260630.xsd#oust_ShareBasedCompensationArrangementByShareBasedPaymentAwardUnvestedRestrictedStockAwardMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e8332-cddc-705a-8ae8-5d38d04d3141" xlink:to="loc_oust_ShareBasedCompensationArrangementByShareBasedPaymentAwardUnvestedRestrictedStockAwardMember_019e8332-cddc-769f-a67d-149dbb2f5deb" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019e8332-cddc-7284-8dfa-1234c25f0470" 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_019e8332-cddc-7dbe-95c2-77901f296950" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019e8332-cddc-7284-8dfa-1234c25f0470" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/RevenueNarrativeDetails" xlink:type="simple" xlink:href="oust-20260630.xsd#RevenueNarrativeDetails"/>
  <link:definitionLink xlink:role="http://ouster.com/role/RevenueNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_019e8332-cddc-7489-b04e-2c45f2bc5eaf" 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_019e8332-cddc-7810-aab7-fc9d9a4b07bf" 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_019e8332-cddc-7489-b04e-2c45f2bc5eaf" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_019e8332-cddc-7810-aab7-fc9d9a4b07bf" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019e8332-cddc-722d-8024-6becbf83fa3e" 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_019e8332-cddc-7810-aab7-fc9d9a4b07bf" xlink:to="loc_srt_ProductOrServiceAxis_019e8332-cddc-722d-8024-6becbf83fa3e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019e8332-cddc-722d-8024-6becbf83fa3e_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_019e8332-cddc-722d-8024-6becbf83fa3e" xlink:to="loc_srt_ProductsAndServicesDomain_019e8332-cddc-722d-8024-6becbf83fa3e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019e8332-cddc-74dd-945f-c848c95992fa" 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_019e8332-cddc-722d-8024-6becbf83fa3e" xlink:to="loc_srt_ProductsAndServicesDomain_019e8332-cddc-74dd-945f-c848c95992fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RoyaltyMember_019e8332-cddc-72d0-b4b8-3d61ec05a955" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RoyaltyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019e8332-cddc-74dd-945f-c848c95992fa" xlink:to="loc_us-gaap_RoyaltyMember_019e8332-cddc-72d0-b4b8-3d61ec05a955" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_MultiYearLicensingContractsMember_019e8332-cddc-7cfa-8d2e-f1a3152350c4" xlink:href="oust-20260630.xsd#oust_MultiYearLicensingContractsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019e8332-cddc-74dd-945f-c848c95992fa" xlink:to="loc_oust_MultiYearLicensingContractsMember_019e8332-cddc-7cfa-8d2e-f1a3152350c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_019e8332-cddc-7389-b9d1-f009687d6557" 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_DisaggregationOfRevenueTable_019e8332-cddc-7810-aab7-fc9d9a4b07bf" xlink:to="loc_srt_MajorCustomersAxis_019e8332-cddc-7389-b9d1-f009687d6557" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019e8332-cddc-7389-b9d1-f009687d6557_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_019e8332-cddc-7389-b9d1-f009687d6557" xlink:to="loc_srt_NameOfMajorCustomerDomain_019e8332-cddc-7389-b9d1-f009687d6557_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019e8332-cddc-71aa-bdf3-a9aa681b842c" 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_019e8332-cddc-7389-b9d1-f009687d6557" xlink:to="loc_srt_NameOfMajorCustomerDomain_019e8332-cddc-71aa-bdf3-a9aa681b842c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_OneCustomerWithMultiyearContractEnteredIn2023Member_019e8332-cddc-75e6-b57d-842c45820080" xlink:href="oust-20260630.xsd#oust_OneCustomerWithMultiyearContractEnteredIn2023Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019e8332-cddc-71aa-bdf3-a9aa681b842c" xlink:to="loc_oust_OneCustomerWithMultiyearContractEnteredIn2023Member_019e8332-cddc-75e6-b57d-842c45820080" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e8332-cddc-74e4-afb3-3a50a8eef6d3" 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_019e8332-cddc-7489-b04e-2c45f2bc5eaf" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e8332-cddc-74e4-afb3-3a50a8eef6d3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetNetCurrent_019e8332-cddc-7aa4-93ac-08e2da41b314" 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_019e8332-cddc-7489-b04e-2c45f2bc5eaf" xlink:to="loc_us-gaap_ContractWithCustomerAssetNetCurrent_019e8332-cddc-7aa4-93ac-08e2da41b314" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_019e8332-cddc-7940-b5f0-de959a24ae33" 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_019e8332-cddc-7489-b04e-2c45f2bc5eaf" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_019e8332-cddc-7940-b5f0-de959a24ae33" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiability_019e8332-cddc-736a-b7ba-e848349c3e5e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e8332-cddc-7489-b04e-2c45f2bc5eaf" xlink:to="loc_us-gaap_ContractWithCustomerLiability_019e8332-cddc-736a-b7ba-e848349c3e5e" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/RevenueScheduleofDisaggregationofRevenueDetails" xlink:type="simple" xlink:href="oust-20260630.xsd#RevenueScheduleofDisaggregationofRevenueDetails"/>
  <link:definitionLink xlink:role="http://ouster.com/role/RevenueScheduleofDisaggregationofRevenueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_019e8332-cddc-7d74-9305-6047601a3aeb" 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_019e8332-cddc-7d65-b75e-84298398ed9c" 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_019e8332-cddc-7d74-9305-6047601a3aeb" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_019e8332-cddc-7d65-b75e-84298398ed9c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_019e8332-cddc-79ab-87b4-98b4d2ac0012" 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_019e8332-cddc-7d65-b75e-84298398ed9c" xlink:to="loc_srt_StatementGeographicalAxis_019e8332-cddc-79ab-87b4-98b4d2ac0012" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019e8332-cddc-79ab-87b4-98b4d2ac0012_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_019e8332-cddc-79ab-87b4-98b4d2ac0012" xlink:to="loc_srt_SegmentGeographicalDomain_019e8332-cddc-79ab-87b4-98b4d2ac0012_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019e8332-cddc-7a59-a2c8-821d321c27b9" 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_019e8332-cddc-79ab-87b4-98b4d2ac0012" xlink:to="loc_srt_SegmentGeographicalDomain_019e8332-cddc-7a59-a2c8-821d321c27b9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AmericasMember_019e8332-cddc-7b7b-9872-8b8bb00e29ce" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_AmericasMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019e8332-cddc-7a59-a2c8-821d321c27b9" xlink:to="loc_srt_AmericasMember_019e8332-cddc-7b7b-9872-8b8bb00e29ce" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AsiaPacificMember_019e8332-cddc-7fac-8b9b-73752f7e30b6" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_AsiaPacificMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019e8332-cddc-7a59-a2c8-821d321c27b9" xlink:to="loc_srt_AsiaPacificMember_019e8332-cddc-7fac-8b9b-73752f7e30b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EMEAMember_019e8332-cddc-7450-8565-4d47221c01a3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EMEAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019e8332-cddc-7a59-a2c8-821d321c27b9" xlink:to="loc_us-gaap_EMEAMember_019e8332-cddc-7450-8565-4d47221c01a3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e8332-cddc-79c3-aec4-d47aaca93546" 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_019e8332-cddc-7d74-9305-6047601a3aeb" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e8332-cddc-79c3-aec4-d47aaca93546" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/RevenueSchedulesofConcentrationofRiskDetails" xlink:type="simple" xlink:href="oust-20260630.xsd#RevenueSchedulesofConcentrationofRiskDetails"/>
  <link:definitionLink xlink:role="http://ouster.com/role/RevenueSchedulesofConcentrationofRiskDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_019e8332-cddc-7c15-b29f-7006718d9540" 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_019e8332-cddc-7a1b-b7ac-dd5740005716" 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_019e8332-cddc-7c15-b29f-7006718d9540" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_019e8332-cddc-7a1b-b7ac-dd5740005716" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_019e8332-cddc-77ed-8b8f-26b98559952b" 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_019e8332-cddc-7a1b-b7ac-dd5740005716" xlink:to="loc_srt_StatementGeographicalAxis_019e8332-cddc-77ed-8b8f-26b98559952b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019e8332-cddc-77ed-8b8f-26b98559952b_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_019e8332-cddc-77ed-8b8f-26b98559952b" xlink:to="loc_srt_SegmentGeographicalDomain_019e8332-cddc-77ed-8b8f-26b98559952b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019e8332-cddc-7c5e-94ce-db8319a5b75f" 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_019e8332-cddc-77ed-8b8f-26b98559952b" xlink:to="loc_srt_SegmentGeographicalDomain_019e8332-cddc-7c5e-94ce-db8319a5b75f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_019e8332-cddc-72ef-b1bf-da4fd1600ec9" 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_019e8332-cddc-7c5e-94ce-db8319a5b75f" xlink:to="loc_country_US_019e8332-cddc-72ef-b1bf-da4fd1600ec9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_TH_019e8332-cddc-767d-8f63-fbc8925ea352" xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_TH"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019e8332-cddc-7c5e-94ce-db8319a5b75f" xlink:to="loc_country_TH_019e8332-cddc-767d-8f63-fbc8925ea352" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019e8332-cddc-7591-829b-be12ab1037e5" 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_DisaggregationOfRevenueTable_019e8332-cddc-7a1b-b7ac-dd5740005716" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019e8332-cddc-7591-829b-be12ab1037e5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e8332-cddc-7591-829b-be12ab1037e5_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_019e8332-cddc-7591-829b-be12ab1037e5" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e8332-cddc-7591-829b-be12ab1037e5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e8332-cddc-78c6-b740-48fb1de2cb75" 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_019e8332-cddc-7591-829b-be12ab1037e5" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e8332-cddc-78c6-b740-48fb1de2cb75" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerMember_019e8332-cddc-749d-9653-ffe7665299a3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e8332-cddc-78c6-b740-48fb1de2cb75" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerMember_019e8332-cddc-749d-9653-ffe7665299a3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_019e8332-cddc-76e3-aae6-f636429ee593" 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_DisaggregationOfRevenueTable_019e8332-cddc-7a1b-b7ac-dd5740005716" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_019e8332-cddc-76e3-aae6-f636429ee593" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019e8332-cddc-76e3-aae6-f636429ee593_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_019e8332-cddc-76e3-aae6-f636429ee593" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019e8332-cddc-76e3-aae6-f636429ee593_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019e8332-cddc-7b90-807e-e54505ed179c" 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_019e8332-cddc-76e3-aae6-f636429ee593" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019e8332-cddc-7b90-807e-e54505ed179c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeographicConcentrationRiskMember_019e8332-cddc-7cab-80c3-1cfd985d3152" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GeographicConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019e8332-cddc-7b90-807e-e54505ed179c" xlink:to="loc_us-gaap_GeographicConcentrationRiskMember_019e8332-cddc-7cab-80c3-1cfd985d3152" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_019e8332-cddc-72ff-8ca2-6fafe9333724" 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_DisaggregationOfRevenueLineItems_019e8332-cddc-7c15-b29f-7006718d9540" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_019e8332-cddc-72ff-8ca2-6fafe9333724" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/RevenueScheduleofContractLiabilitiesDetails" xlink:type="simple" xlink:href="oust-20260630.xsd#RevenueScheduleofContractLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://ouster.com/role/RevenueScheduleofContractLiabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_019e8332-cddc-7163-89b1-2f7d908a53c7" 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_019e8332-cddc-7b20-a61f-199bd0d04bae" 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_019e8332-cddc-7163-89b1-2f7d908a53c7" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_019e8332-cddc-7b20-a61f-199bd0d04bae" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019e8332-cddc-7b20-9baf-048af56a1db0" 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_019e8332-cddc-7b20-a61f-199bd0d04bae" xlink:to="loc_srt_ProductOrServiceAxis_019e8332-cddc-7b20-9baf-048af56a1db0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019e8332-cddc-7b20-9baf-048af56a1db0_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_019e8332-cddc-7b20-9baf-048af56a1db0" xlink:to="loc_srt_ProductsAndServicesDomain_019e8332-cddc-7b20-9baf-048af56a1db0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019e8332-cddc-7dfc-8141-ac9502cdf764" 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_019e8332-cddc-7b20-9baf-048af56a1db0" xlink:to="loc_srt_ProductsAndServicesDomain_019e8332-cddc-7dfc-8141-ac9502cdf764" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_MultiYearLicensingContractsMember_019e8332-cddc-747f-b0f7-21d219613caa" xlink:href="oust-20260630.xsd#oust_MultiYearLicensingContractsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019e8332-cddc-7dfc-8141-ac9502cdf764" xlink:to="loc_oust_MultiYearLicensingContractsMember_019e8332-cddc-747f-b0f7-21d219613caa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_OtherContractsMember_019e8332-cddc-7766-ac7f-1e58d384e1c9" xlink:href="oust-20260630.xsd#oust_OtherContractsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019e8332-cddc-7dfc-8141-ac9502cdf764" xlink:to="loc_oust_OtherContractsMember_019e8332-cddc-7766-ac7f-1e58d384e1c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetNetAbstract_019e8332-cddc-7f75-b6ae-c0118971fa49" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerAssetNetAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e8332-cddc-7163-89b1-2f7d908a53c7" xlink:to="loc_us-gaap_ContractWithCustomerAssetNetAbstract_019e8332-cddc-7f75-b6ae-c0118971fa49" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetNetCurrent_019e8332-cddc-70a9-bdaf-bf0351655b92" 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_ContractWithCustomerAssetNetAbstract_019e8332-cddc-7f75-b6ae-c0118971fa49" xlink:to="loc_us-gaap_ContractWithCustomerAssetNetCurrent_019e8332-cddc-70a9-bdaf-bf0351655b92" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetNetNoncurrent_019e8332-cddc-7d6c-b441-288b083a4a05" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerAssetNetNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContractWithCustomerAssetNetAbstract_019e8332-cddc-7f75-b6ae-c0118971fa49" xlink:to="loc_us-gaap_ContractWithCustomerAssetNetNoncurrent_019e8332-cddc-7d6c-b441-288b083a4a05" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetNet_019e8332-cddc-74c9-a0bb-caba67fc2aab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerAssetNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContractWithCustomerAssetNetAbstract_019e8332-cddc-7f75-b6ae-c0118971fa49" xlink:to="loc_us-gaap_ContractWithCustomerAssetNet_019e8332-cddc-74c9-a0bb-caba67fc2aab" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_ContractWithCustomerLiabilityCurrentAbstract_019e8332-cddc-7060-91bc-1593dd5d4da1" xlink:href="oust-20260630.xsd#oust_ContractWithCustomerLiabilityCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e8332-cddc-7163-89b1-2f7d908a53c7" xlink:to="loc_oust_ContractWithCustomerLiabilityCurrentAbstract_019e8332-cddc-7060-91bc-1593dd5d4da1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_019e8332-cddc-7286-bdd5-54198eac14a5" 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_oust_ContractWithCustomerLiabilityCurrentAbstract_019e8332-cddc-7060-91bc-1593dd5d4da1" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_019e8332-cddc-7286-bdd5-54198eac14a5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_ContractWithCustomerLiabilityNoncurrentAbstract_019e8332-cddc-7ae5-b133-31ce407bc97e" xlink:href="oust-20260630.xsd#oust_ContractWithCustomerLiabilityNoncurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e8332-cddc-7163-89b1-2f7d908a53c7" xlink:to="loc_oust_ContractWithCustomerLiabilityNoncurrentAbstract_019e8332-cddc-7ae5-b133-31ce407bc97e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityNoncurrent_019e8332-cddc-7f15-a552-a9aaa7ada513" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_oust_ContractWithCustomerLiabilityNoncurrentAbstract_019e8332-cddc-7ae5-b133-31ce407bc97e" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityNoncurrent_019e8332-cddc-7f15-a552-a9aaa7ada513" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiability_019e8332-cddc-7f0e-abbc-10fd513c0a8c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e8332-cddc-7163-89b1-2f7d908a53c7" xlink:to="loc_us-gaap_ContractWithCustomerLiability_019e8332-cddc-7f0e-abbc-10fd513c0a8c" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/SegmentNarrativeDetails" xlink:type="simple" xlink:href="oust-20260630.xsd#SegmentNarrativeDetails"/>
  <link:definitionLink xlink:role="http://ouster.com/role/SegmentNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019fa8c2-9306-730e-8d24-aad0cc4ef4ec" 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_019fa8c2-9306-7de6-b56c-607b0ec5ee97" 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_019fa8c2-9306-730e-8d24-aad0cc4ef4ec" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fa8c2-9306-7de6-b56c-607b0ec5ee97" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainContingenciesByNatureAxis_019fa8c2-9306-734e-97d4-c09b469315de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainContingenciesByNatureAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fa8c2-9306-7de6-b56c-607b0ec5ee97" xlink:to="loc_us-gaap_GainContingenciesByNatureAxis_019fa8c2-9306-734e-97d4-c09b469315de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainContingencyNatureDomain_019fa8c2-9306-734e-97d4-c09b469315de_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_GainContingenciesByNatureAxis_019fa8c2-9306-734e-97d4-c09b469315de" xlink:to="loc_us-gaap_GainContingencyNatureDomain_019fa8c2-9306-734e-97d4-c09b469315de_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainContingencyNatureDomain_019fa8c2-9306-789f-b99c-845cae86c4cf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_GainContingenciesByNatureAxis_019fa8c2-9306-734e-97d4-c09b469315de" xlink:to="loc_us-gaap_GainContingencyNatureDomain_019fa8c2-9306-789f-b99c-845cae86c4cf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_IEEPATariffRefundMember_019fa8c2-9306-7d3d-a733-0262b284a361" xlink:href="oust-20260630.xsd#oust_IEEPATariffRefundMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GainContingencyNatureDomain_019fa8c2-9306-789f-b99c-845cae86c4cf" xlink:to="loc_oust_IEEPATariffRefundMember_019fa8c2-9306-7d3d-a733-0262b284a361" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfOperatingSegments_019e8332-cddc-7c14-a0b4-16a46d2e6954" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfOperatingSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fa8c2-9306-730e-8d24-aad0cc4ef4ec" xlink:to="loc_us-gaap_NumberOfOperatingSegments_019e8332-cddc-7c14-a0b4-16a46d2e6954" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportableSegments_019e8332-cddc-7720-b21d-cf9a9e41e08b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfReportableSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fa8c2-9306-730e-8d24-aad0cc4ef4ec" xlink:to="loc_us-gaap_NumberOfReportableSegments_019e8332-cddc-7720-b21d-cf9a9e41e08b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_IEEPATariffRefundClaimsSubmitted_019fb2fe-8a09-74c5-9d21-e7d0d45951ba" xlink:href="oust-20260630.xsd#oust_IEEPATariffRefundClaimsSubmitted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fa8c2-9306-730e-8d24-aad0cc4ef4ec" xlink:to="loc_oust_IEEPATariffRefundClaimsSubmitted_019fb2fe-8a09-74c5-9d21-e7d0d45951ba" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/SegmentsScheduleofSegmentReportingInformationDetails" xlink:type="simple" xlink:href="oust-20260630.xsd#SegmentsScheduleofSegmentReportingInformationDetails"/>
  <link:definitionLink xlink:role="http://ouster.com/role/SegmentsScheduleofSegmentReportingInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019e8332-cddc-7b59-aa6d-4a6aef708475" 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_019e8332-cddc-712d-9ca2-5961f49aedb6" 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_019e8332-cddc-7b59-aa6d-4a6aef708475" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e8332-cddc-712d-9ca2-5961f49aedb6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019e8332-cddc-7ee4-815a-899aa3defd78" 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_019e8332-cddc-712d-9ca2-5961f49aedb6" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019e8332-cddc-7ee4-815a-899aa3defd78" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019e8332-cddc-7ee4-815a-899aa3defd78_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_019e8332-cddc-7ee4-815a-899aa3defd78" xlink:to="loc_us-gaap_SegmentDomain_019e8332-cddc-7ee4-815a-899aa3defd78_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019e8332-cddc-7de0-8049-32ac3b7d0206" 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_019e8332-cddc-7ee4-815a-899aa3defd78" xlink:to="loc_us-gaap_SegmentDomain_019e8332-cddc-7de0-8049-32ac3b7d0206" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_ReportableSegmentMember_019e8332-cddc-7a34-9e19-491035eb2054" xlink:href="oust-20260630.xsd#oust_ReportableSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019e8332-cddc-7de0-8049-32ac3b7d0206" xlink:to="loc_oust_ReportableSegmentMember_019e8332-cddc-7a34-9e19-491035eb2054" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e8332-cddc-7152-836f-c689b9696907" 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_019e8332-cddc-7b59-aa6d-4a6aef708475" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e8332-cddc-7152-836f-c689b9696907" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_019e8332-cddc-759f-adf7-a47190a1374f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e8332-cddc-7b59-aa6d-4a6aef708475" xlink:to="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_019e8332-cddc-759f-adf7-a47190a1374f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ManufacturingCosts_019e8332-cddc-753e-a5db-9a467a7610cf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ManufacturingCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_019e8332-cddc-759f-adf7-a47190a1374f" xlink:to="loc_us-gaap_ManufacturingCosts_019e8332-cddc-753e-a5db-9a467a7610cf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_019e8332-cddc-7ee2-bd7c-5d3c28242dc3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_019e8332-cddc-759f-adf7-a47190a1374f" xlink:to="loc_us-gaap_ShareBasedCompensation_019e8332-cddc-7ee2-bd7c-5d3c28242dc3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCostOfOperatingRevenue_019e8332-cddc-7b2a-a61e-4493360413a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherCostOfOperatingRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_019e8332-cddc-759f-adf7-a47190a1374f" xlink:to="loc_us-gaap_OtherCostOfOperatingRevenue_019e8332-cddc-7b2a-a61e-4493360413a8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_019e8332-cddc-7c2c-9ebe-5ba9ce48eca9" 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_ReconciliationFromSegmentTotalsToConsolidatedAbstract_019e8332-cddc-759f-adf7-a47190a1374f" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_019e8332-cddc-7c2c-9ebe-5ba9ce48eca9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingAndMarketingExpense_019e8332-cddc-7f2d-b780-5473c90254eb" 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_ReconciliationFromSegmentTotalsToConsolidatedAbstract_019e8332-cddc-759f-adf7-a47190a1374f" xlink:to="loc_us-gaap_SellingAndMarketingExpense_019e8332-cddc-7f2d-b780-5473c90254eb" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_019e8332-cddc-78b3-942f-ee5fc63bc044" 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_ReconciliationFromSegmentTotalsToConsolidatedAbstract_019e8332-cddc-759f-adf7-a47190a1374f" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_019e8332-cddc-78b3-942f-ee5fc63bc044" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_019e8332-cddc-7ff4-be5e-c17cabceb19b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_019e8332-cddc-759f-adf7-a47190a1374f" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_019e8332-cddc-7ff4-be5e-c17cabceb19b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_019e8332-cddc-7a54-93b9-9fa3eae6dc88" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_019e8332-cddc-759f-adf7-a47190a1374f" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_019e8332-cddc-7a54-93b9-9fa3eae6dc88" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019e8332-cddc-7d26-bc88-c11830279f43" 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_ReconciliationFromSegmentTotalsToConsolidatedAbstract_019e8332-cddc-759f-adf7-a47190a1374f" xlink:to="loc_us-gaap_NetIncomeLoss_019e8332-cddc-7d26-bc88-c11830279f43" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ouster.com/role/SubsequentEventDetails" xlink:type="simple" xlink:href="oust-20260630.xsd#SubsequentEventDetails"/>
  <link:definitionLink xlink:role="http://ouster.com/role/SubsequentEventDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventLineItems_019fa8c3-c636-790d-ac6e-f5951eef4647" 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_019e8332-ce9d-7a9a-92e0-b2082f6e8ae8" 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_019fa8c3-c636-790d-ac6e-f5951eef4647" xlink:to="loc_us-gaap_SubsequentEventTable_019e8332-ce9d-7a9a-92e0-b2082f6e8ae8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_019fa8c3-c636-7ca9-9652-c9b70e28b876" 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_019e8332-ce9d-7a9a-92e0-b2082f6e8ae8" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_019fa8c3-c636-7ca9-9652-c9b70e28b876" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019fa8c3-c636-7ca9-9652-c9b70e28b876_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_019fa8c3-c636-7ca9-9652-c9b70e28b876" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019fa8c3-c636-7ca9-9652-c9b70e28b876_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019fa8c3-c636-7101-90e8-ba07c62f42a9" 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_019fa8c3-c636-7ca9-9652-c9b70e28b876" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019fa8c3-c636-7101-90e8-ba07c62f42a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_019fa8c3-c636-7d87-8f9c-bee1ded1fbed" 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_019fa8c3-c636-7101-90e8-ba07c62f42a9" xlink:to="loc_us-gaap_SubsequentEventMember_019fa8c3-c636-7d87-8f9c-bee1ded1fbed" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_019fa8c3-c636-7c59-ae76-7af30485d8d7" 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_SubsequentEventTable_019e8332-ce9d-7a9a-92e0-b2082f6e8ae8" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_019fa8c3-c636-7c59-ae76-7af30485d8d7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019fa8c3-c636-7c59-ae76-7af30485d8d7_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_019fa8c3-c636-7c59-ae76-7af30485d8d7" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019fa8c3-c636-7c59-ae76-7af30485d8d7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019fa8c3-c636-7830-930a-07d1b09c9a9b" 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_019fa8c3-c636-7c59-ae76-7af30485d8d7" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019fa8c3-c636-7830-930a-07d1b09c9a9b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_UnderwritingAgreementMember_019fa8c3-c636-7aec-8cf4-0d28934c958c" xlink:href="oust-20260630.xsd#oust_UnderwritingAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019fa8c3-c636-7830-930a-07d1b09c9a9b" xlink:to="loc_oust_UnderwritingAgreementMember_019fa8c3-c636-7aec-8cf4-0d28934c958c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OverAllotmentOptionMember_019fa8c3-c636-7eb2-afc6-a7eaa61dd9b8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OverAllotmentOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019fa8c3-c636-7830-930a-07d1b09c9a9b" xlink:to="loc_us-gaap_OverAllotmentOptionMember_019fa8c3-c636-7eb2-afc6-a7eaa61dd9b8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_PublicOfferingMember_019fa8c3-c636-7d13-ad7d-0cf538d4fd3d" xlink:href="oust-20260630.xsd#oust_PublicOfferingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019fa8c3-c636-7830-930a-07d1b09c9a9b" xlink:to="loc_oust_PublicOfferingMember_019fa8c3-c636-7d13-ad7d-0cf538d4fd3d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_019fa8c3-c636-71fd-a50b-5485a5ff7ba7" 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_SubsequentEventLineItems_019fa8c3-c636-790d-ac6e-f5951eef4647" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_019fa8c3-c636-71fd-a50b-5485a5ff7ba7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_SharesOfferingUnderwritersOptionTerm_019fa8c3-c636-7833-8cf2-61d0df94fa68" xlink:href="oust-20260630.xsd#oust_SharesOfferingUnderwritersOptionTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019fa8c3-c636-790d-ac6e-f5951eef4647" xlink:to="loc_oust_SharesOfferingUnderwritersOptionTerm_019fa8c3-c636-7833-8cf2-61d0df94fa68" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesIssuedPricePerShare_019fa8c3-c636-7dbb-bbad-47b64c71266a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesIssuedPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019fa8c3-c636-790d-ac6e-f5951eef4647" xlink:to="loc_us-gaap_SharesIssuedPricePerShare_019fa8c3-c636-7dbb-bbad-47b64c71266a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019fa8c3-c636-7c97-981b-224dc83bef9e" 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_SubsequentEventLineItems_019fa8c3-c636-790d-ac6e-f5951eef4647" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019fa8c3-c636-7c97-981b-224dc83bef9e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_019fa8c3-c636-76a6-a481-ad1dcd045f27" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019fa8c3-c636-790d-ac6e-f5951eef4647" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_019fa8c3-c636-76a6-a481-ad1dcd045f27" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/IndividualsOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2026/ecd-2026.xsd#IndividualsOnly"/>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/ecd/role/IndividualsOnly" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ecd_AllIndividualsMember" xlink:href="https://xbrl.sec.gov/ecd/2026/ecd-2026.xsd#ecd_AllIndividualsMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_KennethGianellaMember_019f8fdb-84f1-7087-a34b-4554620cfcda" xlink:href="oust-20260630.xsd#oust_KennethGianellaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllIndividualsMember" xlink:to="loc_oust_KennethGianellaMember_019f8fdb-84f1-7087-a34b-4554620cfcda" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_oust_MeganChungMember_019f8fde-bf4a-738b-8c07-08ded1f91328" xlink:href="oust-20260630.xsd#oust_MeganChungMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllIndividualsMember" xlink:to="loc_oust_MeganChungMember_019f8fde-bf4a-738b-8c07-08ded1f91328" xlink:type="arc" order="3"/>
  </link:definitionLink>
</link:linkbase>
