3.25.4 html 117 357 1 true 39 0 false 8 false false R1.htm 75000 - Document - Document and Entity Information Sheet http://boundlessbio.com/20251231/taxonomy/role/DocumentDocumentAndEntityInformation Document and Entity Information Cover 1 false false R2.htm 75010 - Statement - Balance Sheets Sheet http://boundlessbio.com/20251231/taxonomy/role/StatementBalanceSheets Balance Sheets Statements 2 false false R3.htm 75020 - Statement - Balance Sheets (Parenthetical) Sheet http://boundlessbio.com/20251231/taxonomy/role/StatementBalanceSheetsParenthetical Balance Sheets (Parenthetical) Statements 3 false false R4.htm 75030 - Statement - Statements of Operations and Comprehensive Loss Sheet http://boundlessbio.com/20251231/taxonomy/role/StatementStatementsOfOperationsAndComprehensiveLoss Statements of Operations and Comprehensive Loss Statements 4 false false R5.htm 75040 - Statement - Statements of Convertible Preferred Stock and Stockholders' Equity Sheet http://boundlessbio.com/20251231/taxonomy/role/StatementStatementsOfConvertiblePreferredStockAndStockholdersEquity1 Statements of Convertible Preferred Stock and Stockholders' Equity Statements 5 false false R6.htm 75050 - Statement - Statements of Convertible Preferred Stock and Stockholders' Equity (Parenthetical) Sheet http://boundlessbio.com/20251231/taxonomy/role/StatementStatementsOfConvertiblePreferredStockAndStockholdersEquityParenthetical Statements of Convertible Preferred Stock and Stockholders' Equity (Parenthetical) Statements 6 false false R7.htm 75060 - Statement - Statements of Cash Flows Sheet http://boundlessbio.com/20251231/taxonomy/role/StatementStatementsOfCashFlows Statements of Cash Flows Statements 7 false false R8.htm 995410 - Disclosure - Pay vs Performance Disclosure Sheet http://xbrl.sec.gov/ecd/role/PvpDisclosure Pay vs Performance Disclosure Notes 8 false false R9.htm 995445 - Disclosure - Insider Trading Arrangements Sheet http://xbrl.sec.gov/ecd/role/InsiderTradingArrangements Insider Trading Arrangements Notes 9 false false R10.htm 995455 - Disclosure - Cybersecurity Risk Management, Strategy, and Governance Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureCybersecurityRiskManagementStrategyAndGovernance Cybersecurity Risk Management, Strategy, and Governance Notes 10 false false R11.htm 995465 - Disclosure - Organization and Basis of Presentation Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureOrganizationAndBasisOfPresentation Organization and Basis of Presentation Notes 11 false false R12.htm 995475 - Disclosure - Summary of Significant Accounting Policies Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureSummaryOfSignificantAccountingPolicies Summary of Significant Accounting Policies Notes 12 false false R13.htm 995485 - Disclosure - Fair Value Measurements Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureFairValueMeasurements Fair Value Measurements Notes 13 false false R14.htm 995495 - Disclosure - Investments Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureInvestments Investments Notes 14 false false R15.htm 995505 - Disclosure - Property and Equipment Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosurePropertyAndEquipment1 Property and Equipment Notes 15 false false R16.htm 995515 - Disclosure - Accounts Payable and Accrued Liabilities Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureAccountsPayableAndAccruedLiabilities Accounts Payable and Accrued Liabilities Notes 16 false false R17.htm 995525 - Disclosure - Lease Agreements Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureLeaseAgreements Lease Agreements Notes 17 false false R18.htm 995535 - Disclosure - Commitments and Contingencies Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureCommitmentsAndContingencies Commitments and Contingencies Notes 18 false false R19.htm 995555 - Disclosure - Common Stock Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureCommonStock Common Stock Notes 19 false false R20.htm 995565 - Disclosure - Stock-Based Compensation Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureStockbasedCompensation Stock-Based Compensation Notes 20 false false R21.htm 995575 - Disclosure - Income Taxes Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureIncomeTaxes Income Taxes Notes 21 false false R22.htm 995585 - Disclosure - Net Loss Per Common Share Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureNetLossPerCommonShare Net Loss Per Common Share Notes 22 false false R23.htm 995595 - Disclosure - Segment Information Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureSegmentInformation Segment Information Notes 23 false false R24.htm 995615 - Disclosure - Summary of Significant Accounting Policies (Policies) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesPolicies Summary of Significant Accounting Policies (Policies) Policies http://boundlessbio.com/20251231/taxonomy/role/DisclosureSummaryOfSignificantAccountingPolicies 24 false false R25.htm 995625 - Disclosure - Fair Value Measurements (Tables) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureFairValueMeasurementsTables Fair Value Measurements (Tables) Tables http://boundlessbio.com/20251231/taxonomy/role/DisclosureFairValueMeasurements 25 false false R26.htm 995635 - Disclosure - Investments (Tables) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureInvestmentsTables Investments (Tables) Tables http://boundlessbio.com/20251231/taxonomy/role/DisclosureInvestments 26 false false R27.htm 995645 - Disclosure - Property and Equipment (Tables) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosurePropertyAndEquipmentTables Property and Equipment (Tables) Tables http://boundlessbio.com/20251231/taxonomy/role/DisclosurePropertyAndEquipment1 27 false false R28.htm 995655 - Disclosure - Accounts Payable and Accrued Liabilities (Tables) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureAccountsPayableAndAccruedLiabilitiesTables Accounts Payable and Accrued Liabilities (Tables) Tables http://boundlessbio.com/20251231/taxonomy/role/DisclosureAccountsPayableAndAccruedLiabilities 28 false false R29.htm 995665 - Disclosure - Lease Agreements (Tables) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureLeaseAgreementsTables Lease Agreements (Tables) Tables http://boundlessbio.com/20251231/taxonomy/role/DisclosureLeaseAgreements 29 false false R30.htm 995685 - Disclosure - Common Stock (Tables) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureCommonStockTables Common Stock (Tables) Tables http://boundlessbio.com/20251231/taxonomy/role/DisclosureCommonStock 30 false false R31.htm 995695 - Disclosure - Stock-Based Compensation (Tables) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureStockbasedCompensationTables Stock-Based Compensation (Tables) Tables http://boundlessbio.com/20251231/taxonomy/role/DisclosureStockbasedCompensation 31 false false R32.htm 995705 - Disclosure - Income Taxes (Tables) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureIncomeTaxesTables Income Taxes (Tables) Tables http://boundlessbio.com/20251231/taxonomy/role/DisclosureIncomeTaxes 32 false false R33.htm 995715 - Disclosure - Net Loss Per Common Share (Tables) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureNetLossPerCommonShareTables Net Loss Per Common Share (Tables) Tables http://boundlessbio.com/20251231/taxonomy/role/DisclosureNetLossPerCommonShare 33 false false R34.htm 995725 - Disclosure - Segment Information (Tables) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureSegmentInformationTables Segment Information (Tables) Tables http://boundlessbio.com/20251231/taxonomy/role/DisclosureSegmentInformation 34 false false R35.htm 995745 - Disclosure - Organization and Basis of Presentation - Additional Information (Details) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureOrganizationAndBasisOfPresentationAdditionalInformationDetails Organization and Basis of Presentation - Additional Information (Details) Details 35 false false R36.htm 995755 - Disclosure - Summary of Significant Accounting Policies - Additional Information (Details) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetails Summary of Significant Accounting Policies - Additional Information (Details) Details 36 false false R37.htm 995765 - Disclosure - Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on Recurring Basis (Details) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfFinancialAssetsMeasuredAtFairValueOnRecurringBasisDetails Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on Recurring Basis (Details) Details 37 false false R38.htm 995775 - Disclosure - Fair Value Measurements - Additional Information (Details) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureFairValueMeasurementsAdditionalInformationDetails Fair Value Measurements - Additional Information (Details) Details 38 false false R39.htm 995785 - Disclosure - Investments - Schedule of Available-for-Sale Securities (Details) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureInvestmentsScheduleOfAvailableforsaleSecuritiesDetails Investments - Schedule of Available-for-Sale Securities (Details) Details 39 false false R40.htm 995795 - Disclosure - Investments - Additional Information (Details) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureInvestmentsAdditionalInformationDetails Investments - Additional Information (Details) Details 40 false false R41.htm 995805 - Disclosure - Property and Equipment - Summary of Property and Equipment, Net (Details) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosurePropertyAndEquipmentSummaryOfPropertyAndEquipmentNetDetails Property and Equipment - Summary of Property and Equipment, Net (Details) Details 41 false false R42.htm 995815 - Disclosure - Property and Equipment - Additional Information (Details) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosurePropertyAndEquipmentAdditionalInformationDetails Property and Equipment - Additional Information (Details) Details 42 false false R43.htm 995825 - Disclosure - Accounts Payable and Accrued Liabilities - Schedule of Accounts Payable and Accrued Liabilities (Details) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureAccountsPayableAndAccruedLiabilitiesScheduleOfAccountsPayableAndAccruedLiabilitiesDetails Accounts Payable and Accrued Liabilities - Schedule of Accounts Payable and Accrued Liabilities (Details) Details 43 false false R44.htm 995835 - Disclosure - Lease Agreements - Additional Information (Details) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureLeaseAgreementsAdditionalInformationDetails Lease Agreements - Additional Information (Details) Details 44 false false R45.htm 995845 - Disclosure - Lease Agreements - Schedule of Future Undiscounted Operating Lease Payments (Details) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureLeaseAgreementsScheduleOfFutureUndiscountedOperatingLeasePaymentsDetails Lease Agreements - Schedule of Future Undiscounted Operating Lease Payments (Details) Details 45 false false R46.htm 995865 - Disclosure - Common Stock - Additional Information (Details) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureCommonStockAdditionalInformationDetails Common Stock - Additional Information (Details) Details 46 false false R47.htm 995875 - Disclosure - Common Stock - Schedule of Common Stock Reserved for Future Issuance (Details) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureCommonStockScheduleOfCommonStockReservedForFutureIssuanceDetails Common Stock - Schedule of Common Stock Reserved for Future Issuance (Details) Details 47 false false R48.htm 995885 - Disclosure - Stock-Based Compensation - Additional Information (Details) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureStockbasedCompensationAdditionalInformationDetails Stock-Based Compensation - Additional Information (Details) Details 48 false false R49.htm 995895 - Disclosure - Stock-Based Compensation - Schedule of Stock Option Activity Under the Plan and the Predecessor Plan (Details) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureStockbasedCompensationScheduleOfStockOptionActivityUnderThePlanAndThePredecessorPlanDetails Stock-Based Compensation - Schedule of Stock Option Activity Under the Plan and the Predecessor Plan (Details) Details 49 false false R50.htm 995905 - Disclosure - Stock-Based Compensation - Schedule of Stock-based Compensation Expense (Details) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureStockbasedCompensationScheduleOfStockbasedCompensationExpenseDetails Stock-Based Compensation - Schedule of Stock-based Compensation Expense (Details) Details 50 false false R51.htm 995915 - Disclosure - Stock-Based Compensation - Schedule of Excluding Any Effect of the Option Repricing, Weighted-average Assumptions Used in the Black-Scholes Option Pricing Model to Determine the Fair Value of the Stock Options Granted (Details) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureStockbasedCompensationScheduleOfExcludingAnyEffectOfTheOptionRepricingWeightedaverageAssumptionsUsedInTheBlackscholesOptionPricin Stock-Based Compensation - Schedule of Excluding Any Effect of the Option Repricing, Weighted-average Assumptions Used in the Black-Scholes Option Pricing Model to Determine the Fair Value of the Stock Options Granted (Details) Details 51 false false R52.htm 995925 - Disclosure - Income Taxes - Additional Information (Details) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureIncomeTaxesAdditionalInformationDetails Income Taxes - Additional Information (Details) Details 52 false false R53.htm 995935 - Disclosure - Income Taxes - Schedule of Reconciliation of Effective Tax Rate (Details) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureIncomeTaxesScheduleOfReconciliationOfEffectiveTaxRateDetails Income Taxes - Schedule of Reconciliation of Effective Tax Rate (Details) Details 53 false false R54.htm 995945 - Disclosure - Income Taxes - Schedule of Significant Components of Deferred Income Taxes (Details) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureIncomeTaxesScheduleOfSignificantComponentsOfDeferredIncomeTaxesDetails Income Taxes - Schedule of Significant Components of Deferred Income Taxes (Details) Details 54 false false R55.htm 995955 - Disclosure - Income Taxes - Schedule of Activity in Valuation Allowance (Details) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureIncomeTaxesScheduleOfActivityInValuationAllowanceDetails Income Taxes - Schedule of Activity in Valuation Allowance (Details) Details 55 false false R56.htm 995965 - Disclosure - Income Taxes - Summary of Net Operating Loss Carryforwards (Details) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureIncomeTaxesSummaryOfNetOperatingLossCarryforwardsDetails Income Taxes - Summary of Net Operating Loss Carryforwards (Details) Details 56 false false R57.htm 995975 - Disclosure - Income Taxes - Summary of Gross Unrecognized Tax Benefits (Details) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureIncomeTaxesSummaryOfGrossUnrecognizedTaxBenefitsDetails Income Taxes - Summary of Gross Unrecognized Tax Benefits (Details) Details 57 false false R58.htm 995985 - Disclosure - Net Loss Per Common Share - Summary of Basic and Diluted Net Loss Per Common Share (Details) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureNetLossPerCommonShareSummaryOfBasicAndDilutedNetLossPerCommonShareDetails Net Loss Per Common Share - Summary of Basic and Diluted Net Loss Per Common Share (Details) Details 58 false false R59.htm 995995 - Disclosure - Net Loss Per Common Share - Additional Information (Details) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureNetLossPerCommonShareAdditionalInformationDetails Net Loss Per Common Share - Additional Information (Details) Details 59 false false R60.htm 996005 - Disclosure - Segment Information - Schedule of Segment Loss (Details) Sheet http://boundlessbio.com/20251231/taxonomy/role/DisclosureSegmentInformationScheduleOfSegmentLossDetails Segment Information - Schedule of Segment Loss (Details) Details 60 false false All Reports Book All Reports bold-20251231.htm bold-20251231.xsd img75111675_0.gif img75111675_1.gif img75111675_10.jpg img75111675_11.gif img75111675_12.gif img75111675_13.jpg img75111675_14.gif img75111675_15.jpg img75111675_16.gif img75111675_17.gif img75111675_18.jpg img75111675_19.gif img75111675_2.jpg img75111675_20.gif img75111675_21.gif img75111675_22.gif img75111675_23.gif img75111675_24.gif img75111675_3.jpg img75111675_4.jpg img75111675_5.jpg img75111675_6.jpg img75111675_7.jpg img75111675_8.gif img75111675_9.jpg http://fasb.org/us-gaap/2025 http://xbrl.sec.gov/cyd/2025 http://xbrl.sec.gov/dei/2025 http://xbrl.sec.gov/ecd/2025 false false