3.26.1 html 172 233 1 false 45 0 false 4 false false R1.htm 1001 - Document - Cover Page Sheet http://www.cyclerion.com/role/CoverPage Cover Page Cover 1 false false R2.htm 1002 - Statement - Condensed Consolidated Balance Sheets Sheet http://www.cyclerion.com/role/CondensedConsolidatedBalanceSheets Condensed Consolidated Balance Sheets Statements 2 false false R3.htm 1003 - Statement - Condensed Consolidated Balance Sheets (Parenthetical) Sheet http://www.cyclerion.com/role/CondensedConsolidatedBalanceSheetsParenthetical Condensed Consolidated Balance Sheets (Parenthetical) Statements 3 false false R4.htm 1004 - Statement - Condensed Consolidated Statements of Operations and Comprehensive Loss Sheet http://www.cyclerion.com/role/CondensedConsolidatedStatementsOfOperationsAndComprehensiveLoss Condensed Consolidated Statements of Operations and Comprehensive Loss Statements 4 false false R5.htm 1005 - Statement - Condensed Consolidated Statements of Stockholders' Equity Sheet http://www.cyclerion.com/role/CondensedConsolidatedStatementsOfStockholdersEquity Condensed Consolidated Statements of Stockholders' Equity Statements 5 false false R6.htm 1006 - Statement - Condensed Consolidated Statements of Cash Flows Sheet http://www.cyclerion.com/role/CondensedConsolidatedStatementsOfCashFlows Condensed Consolidated Statements of Cash Flows Statements 6 false false R7.htm 1007 - Disclosure - Nature of Business Sheet http://www.cyclerion.com/role/NatureOfBusiness Nature of Business Notes 7 false false R8.htm 1008 - Disclosure - Summary of Significant Accounting Policies Sheet http://www.cyclerion.com/role/SummaryOfSignificantAccountingPolicies Summary of Significant Accounting Policies Notes 8 false false R9.htm 1009 - Disclosure - Fair Value of Financial Instruments Sheet http://www.cyclerion.com/role/FairValueOfFinancialInstruments Fair Value of Financial Instruments Notes 9 false false R10.htm 1010 - Disclosure - Other Investment Sheet http://www.cyclerion.com/role/OtherInvestment Other Investment Notes 10 false false R11.htm 1011 - Disclosure - Accrued Expenses and Other Current Liabilities Sheet http://www.cyclerion.com/role/AccruedExpensesAndOtherCurrentLiabilities Accrued Expenses and Other Current Liabilities Notes 11 false false R12.htm 1012 - Disclosure - Commitments and Contingencies Sheet http://www.cyclerion.com/role/CommitmentsAndContingencies Commitments and Contingencies Notes 12 false false R13.htm 1013 - Disclosure - Share-based Compensation Plans Sheet http://www.cyclerion.com/role/ShareBasedCompensationPlans Share-based Compensation Plans Notes 13 false false R14.htm 1014 - Disclosure - Loss per share Sheet http://www.cyclerion.com/role/LossPerShare Loss per share Notes 14 false false R15.htm 1015 - Disclosure - Income Taxes Sheet http://www.cyclerion.com/role/IncomeTaxes Income Taxes Notes 15 false false R16.htm 1016 - Disclosure - Defined Contribution Plan Sheet http://www.cyclerion.com/role/DefinedContributionPlan Defined Contribution Plan Notes 16 false false R17.htm 1017 - Disclosure - License and Option Agreement Sheet http://www.cyclerion.com/role/LicenseAndOptionAgreement License and Option Agreement Notes 17 false false R18.htm 1018 - Disclosure - Subsequent Events Sheet http://www.cyclerion.com/role/SubsequentEvents Subsequent Events Notes 18 false false R19.htm 1019 - Disclosure - Summary of Significant Accounting Policies (Policies) Sheet http://www.cyclerion.com/role/SummaryOfSignificantAccountingPoliciesPolicies Summary of Significant Accounting Policies (Policies) Policies http://www.cyclerion.com/role/SummaryOfSignificantAccountingPolicies 19 false false R20.htm 1020 - Disclosure - Fair Value of Financial Instruments (Tables) Sheet http://www.cyclerion.com/role/FairValueOfFinancialInstrumentsTables Fair Value of Financial Instruments (Tables) Tables http://www.cyclerion.com/role/FairValueOfFinancialInstruments 20 false false R21.htm 1021 - Disclosure - Accrued Expenses and Other Current Liabilities (Tables) Sheet http://www.cyclerion.com/role/AccruedExpensesAndOtherCurrentLiabilitiesTables Accrued Expenses and Other Current Liabilities (Tables) Tables http://www.cyclerion.com/role/AccruedExpensesAndOtherCurrentLiabilities 21 false false R22.htm 1022 - Disclosure - Share-based Compensation Plans (Tables) Sheet http://www.cyclerion.com/role/ShareBasedCompensationPlansTables Share-based Compensation Plans (Tables) Tables http://www.cyclerion.com/role/ShareBasedCompensationPlans 22 false false R23.htm 1023 - Disclosure - Loss per share (Tables) Sheet http://www.cyclerion.com/role/LossPerShareTables Loss per share (Tables) Tables http://www.cyclerion.com/role/LossPerShare 23 false false R24.htm 1024 - Disclosure - Income Taxes (Tables) Sheet http://www.cyclerion.com/role/IncomeTaxesTables Income Taxes (Tables) Tables http://www.cyclerion.com/role/IncomeTaxes 24 false false R25.htm 1025 - Disclosure - Nature of Business (Details) Sheet http://www.cyclerion.com/role/NatureOfBusinessDetails Nature of Business (Details) Details http://www.cyclerion.com/role/NatureOfBusiness 25 false false R26.htm 1026 - Disclosure - Summary of Significant Accounting Policies - Revenue, Patent Costs, and Interest and Other Income (Details) Sheet http://www.cyclerion.com/role/SummaryOfSignificantAccountingPoliciesRevenuePatentCostsAndInterestAndOtherIncomeDetails Summary of Significant Accounting Policies - Revenue, Patent Costs, and Interest and Other Income (Details) Details 26 false false R27.htm 1027 - Disclosure - Summary of Significant Accounting Policies - Income Taxes (Details) Sheet http://www.cyclerion.com/role/SummaryOfSignificantAccountingPoliciesIncomeTaxesDetails Summary of Significant Accounting Policies - Income Taxes (Details) Details 27 false false R28.htm 1028 - Disclosure - Fair Value of Financial Instruments (Details) Sheet http://www.cyclerion.com/role/FairValueOfFinancialInstrumentsDetails Fair Value of Financial Instruments (Details) Details http://www.cyclerion.com/role/FairValueOfFinancialInstrumentsTables 28 false false R29.htm 1029 - Disclosure - Other Investment - Additional Information (Details) Sheet http://www.cyclerion.com/role/OtherInvestmentAdditionalInformationDetails Other Investment - Additional Information (Details) Details 29 false false R30.htm 1030 - Disclosure - Accrued Expenses and Other Current Liabilities (Details) Sheet http://www.cyclerion.com/role/AccruedExpensesAndOtherCurrentLiabilitiesDetails Accrued Expenses and Other Current Liabilities (Details) Details http://www.cyclerion.com/role/AccruedExpensesAndOtherCurrentLiabilitiesTables 30 false false R31.htm 1031 - Disclosure - Commitments and Contingencies - Additional Information (Details) Sheet http://www.cyclerion.com/role/CommitmentsAndContingenciesAdditionalInformationDetails Commitments and Contingencies - Additional Information (Details) Details 31 false false R32.htm 1032 - Disclosure - Share-based Compensation Plans (Details) Sheet http://www.cyclerion.com/role/ShareBasedCompensationPlansDetails Share-based Compensation Plans (Details) Details http://www.cyclerion.com/role/ShareBasedCompensationPlansTables 32 false false R33.htm 1033 - Disclosure - Share-based Compensation Plans - Schedule of Share-based Compensation Expense (Details) Sheet http://www.cyclerion.com/role/ShareBasedCompensationPlansScheduleOfShareBasedCompensationExpenseDetails Share-based Compensation Plans - Schedule of Share-based Compensation Expense (Details) Details 33 false false R34.htm 1034 - Disclosure - Share-based Compensation Plans - Schedule of Stock Option Activity (Details) Sheet http://www.cyclerion.com/role/ShareBasedCompensationPlansScheduleOfStockOptionActivityDetails Share-based Compensation Plans - Schedule of Stock Option Activity (Details) Details 34 false false R35.htm 1035 - Disclosure - Share-based Compensation Plans - Schedule of Weighted Average Assumptions used in estimating the fair value of the stock options (Details) Sheet http://www.cyclerion.com/role/ShareBasedCompensationPlansScheduleOfWeightedAverageAssumptionsUsedInEstimatingTheFairValueOfTheStockOptionsDetails Share-based Compensation Plans - Schedule of Weighted Average Assumptions used in estimating the fair value of the stock options (Details) Details 35 false false R36.htm 1036 - Disclosure - Share-based Compensation Plans - Summary of RSA activity (Details) Sheet http://www.cyclerion.com/role/ShareBasedCompensationPlansSummaryOfRsaActivityDetails Share-based Compensation Plans - Summary of RSA activity (Details) Details 36 false false R37.htm 1037 - Disclosure - Loss per share - Schedule of Basic and Diluted Net Loss Per Common Share (Details) Sheet http://www.cyclerion.com/role/LossPerShareScheduleOfBasicAndDilutedNetLossPerCommonShareDetails Loss per share - Schedule of Basic and Diluted Net Loss Per Common Share (Details) Details 37 false false R38.htm 1038 - Disclosure - Loss per share - Schedule Of Earnings Per Share Diluted By Common Class (Details) Sheet http://www.cyclerion.com/role/LossPerShareScheduleOfEarningsPerShareDilutedByCommonClassDetails Loss per share - Schedule Of Earnings Per Share Diluted By Common Class (Details) Details 38 false false R39.htm 1039 - Disclosure - Income Taxes - Schedule of Components of Net Income Loss Before Income Tax Expense (Details) Sheet http://www.cyclerion.com/role/IncomeTaxesScheduleOfComponentsOfNetIncomeLossBeforeIncomeTaxExpenseDetails Income Taxes - Schedule of Components of Net Income Loss Before Income Tax Expense (Details) Details 39 false false R40.htm 1040 - Disclosure - Income Taxes - Additional Information (Details) Sheet http://www.cyclerion.com/role/IncomeTaxesAdditionalInformationDetails Income Taxes - Additional Information (Details) Details 40 false false R41.htm 1041 - Disclosure - Income Taxes - Reconciliation of income taxes (Details) Sheet http://www.cyclerion.com/role/IncomeTaxesReconciliationOfIncomeTaxesDetails Income Taxes - Reconciliation of income taxes (Details) Details 41 false false R42.htm 1042 - Disclosure - Income Taxes - Deferred tax assets (liabilities) (Details) Sheet http://www.cyclerion.com/role/IncomeTaxesDeferredTaxAssetsLiabilitiesDetails Income Taxes - Deferred tax assets (liabilities) (Details) Details 42 false false R43.htm 1043 - Disclosure - Defined Contribution Plan (Details) Sheet http://www.cyclerion.com/role/DefinedContributionPlanDetails Defined Contribution Plan (Details) Details http://www.cyclerion.com/role/DefinedContributionPlan 43 false false R44.htm 1044 - Disclosure - License and Option Agreement - Additional Information (Details) Sheet http://www.cyclerion.com/role/LicenseAndOptionAgreementAdditionalInformationDetails License and Option Agreement - Additional Information (Details) Details 44 false false R45.htm 1045 - Disclosure - Subsequent Events (Additional Information) (Details) Sheet http://www.cyclerion.com/role/SubsequentEventsAdditionalInformationDetails Subsequent Events (Additional Information) (Details) Details http://www.cyclerion.com/role/SubsequentEvents 45 false false All Reports Book All Reports ck0001755237-20260331.xsd d111069ds4a.htm g111069g00a01.jpg g111069g00a02.jpg g111069g00a03.jpg g111069g00a04.jpg g111069g00a05.jpg g111069g00a06.jpg g111069g00a07.jpg g111069g00a08.jpg g111069g00a09.jpg g111069g00a10.jpg g111069g00a11.jpg g111069g00a12.jpg g111069g00a13.jpg g111069g00a14.jpg g111069g00a15.jpg g111069g00a16.jpg g111069g55a01.jpg g111069g55a02.jpg g111069g55a03.jpg g111069g55z04.jpg g111069g99a01.jpg g111069g99a02.jpg g111069g99a03.jpg g111069g99a04.jpg g111069g99a05.jpg g111069g99a06.jpg g111069g99a07.jpg g111069g99a08.jpg http://fasb.org/us-gaap/2025 http://xbrl.sec.gov/dei/2025 false false