3.25.2 html 191 252 1 false 53 0 false 6 false false R1.htm 75000 - Document - Cover Page Sheet http://annexonbio.com/20250630/taxonomy/role/Role_DocumentCoverPage Cover Page Cover 1 false false R2.htm 75010 - Statement - Condensed Consolidated Balance Sheets Sheet http://annexonbio.com/20250630/taxonomy/role/Role_StatementCondensedConsolidatedBalanceSheets Condensed Consolidated Balance Sheets Statements 2 false false R3.htm 75020 - Statement - Condensed Consolidated Statements of Operations Sheet http://annexonbio.com/20250630/taxonomy/role/Role_StatementCondensedConsolidatedStatementsOfOperations Condensed Consolidated Statements of Operations Statements 3 false false R4.htm 75030 - Statement - Condensed Consolidated Statements of Comprehensive Loss Sheet http://annexonbio.com/20250630/taxonomy/role/Role_StatementCondensedConsolidatedStatementsOfComprehensiveLoss Condensed Consolidated Statements of Comprehensive Loss Statements 4 false false R5.htm 75040 - Statement - Condensed Consolidated Statements of Stockholders' Equity Sheet http://annexonbio.com/20250630/taxonomy/role/Role_StatementCondensedConsolidatedStatementsOfStockholdersEquity Condensed Consolidated Statements of Stockholders' Equity Statements 5 false false R6.htm 75050 - Statement - Condensed Consolidated Statements of Stockholders' Equity (Parenthetical) Sheet http://annexonbio.com/20250630/taxonomy/role/StatementCondensedConsolidatedStatementsOfStockholdersEquityParenthetical Condensed Consolidated Statements of Stockholders' Equity (Parenthetical) Statements 6 false false R7.htm 75060 - Statement - Condensed Consolidated Statements of Cash Flows Sheet http://annexonbio.com/20250630/taxonomy/role/Role_StatementCondensedConsolidatedStatementsOfCashFlows Condensed Consolidated 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 - Organization Sheet http://annexonbio.com/20250630/taxonomy/role/Role_DisclosureOrganization Organization Notes 10 false false R11.htm 995465 - Disclosure - Basis of Presentation and Significant Accounting Policies Sheet http://annexonbio.com/20250630/taxonomy/role/Role_DisclosureBasisOfPresentationAndSignificantAccountingPolicies Basis of Presentation and Significant Accounting Policies Notes 11 false false R12.htm 995475 - Disclosure - Fair Value Measurements Sheet http://annexonbio.com/20250630/taxonomy/role/Role_DisclosureFairValueMeasurements Fair Value Measurements Notes 12 false false R13.htm 995485 - Disclosure - Balance Sheet Components Sheet http://annexonbio.com/20250630/taxonomy/role/Role_DisclosureBalanceSheetComponents Balance Sheet Components Notes 13 false false R14.htm 995495 - Disclosure - Commitments and Contingencies Sheet http://annexonbio.com/20250630/taxonomy/role/Role_DisclosureCommitmentsAndContingencies Commitments and Contingencies Notes 14 false false R15.htm 995505 - Disclosure - Stockholders' Equity Sheet http://annexonbio.com/20250630/taxonomy/role/DisclosureStockholdersEquity1 Stockholders' Equity Notes 15 false false R16.htm 995515 - Disclosure - Equity Incentive Plans Sheet http://annexonbio.com/20250630/taxonomy/role/DisclosureEquityIncentivePlans Equity Incentive Plans Notes 16 false false R17.htm 995555 - Disclosure - Net Loss Per Share Sheet http://annexonbio.com/20250630/taxonomy/role/DisclosureNetLossPerShare1 Net Loss Per Share Notes 17 false false R18.htm 995565 - Disclosure - Segment Reporting Sheet http://annexonbio.com/20250630/taxonomy/role/DisclosureSegmentReporting Segment Reporting Notes 18 false false R19.htm 995585 - Disclosure - Basis of Presentation and Significant Accounting Policies (Policies) Sheet http://annexonbio.com/20250630/taxonomy/role/Role_DisclosureBasisOfPresentationAndSignificantAccountingPoliciesPolicies Basis of Presentation and Significant Accounting Policies (Policies) Policies http://annexonbio.com/20250630/taxonomy/role/Role_DisclosureBasisOfPresentationAndSignificantAccountingPolicies 19 false false R20.htm 995595 - Disclosure - Fair Value Measurements (Tables) Sheet http://annexonbio.com/20250630/taxonomy/role/Role_DisclosureFairValueMeasurementsTables Fair Value Measurements (Tables) Tables http://annexonbio.com/20250630/taxonomy/role/Role_DisclosureFairValueMeasurements 20 false false R21.htm 995605 - Disclosure - Balance Sheet Components (Tables) Sheet http://annexonbio.com/20250630/taxonomy/role/Role_DisclosureBalanceSheetComponentsTables Balance Sheet Components (Tables) Tables http://annexonbio.com/20250630/taxonomy/role/Role_DisclosureBalanceSheetComponents 21 false false R22.htm 995615 - Disclosure - Commitments and Contingencies (Tables) Sheet http://annexonbio.com/20250630/taxonomy/role/Role_DisclosureCommitmentsAndContingenciesTables Commitments and Contingencies (Tables) Tables http://annexonbio.com/20250630/taxonomy/role/Role_DisclosureCommitmentsAndContingencies 22 false false R23.htm 995625 - Disclosure - Stockholders' Equity (Tables) Sheet http://annexonbio.com/20250630/taxonomy/role/DisclosureStockholdersEquityTables Stockholders' Equity (Tables) Tables http://annexonbio.com/20250630/taxonomy/role/DisclosureStockholdersEquity1 23 false false R24.htm 995635 - Disclosure - Equity Incentive Plans (Tables) Sheet http://annexonbio.com/20250630/taxonomy/role/DisclosureEquityIncentivePlansTables Equity Incentive Plans (Tables) Tables http://annexonbio.com/20250630/taxonomy/role/DisclosureEquityIncentivePlans 24 false false R25.htm 995645 - Disclosure - Net Loss Per Share (Tables) Sheet http://annexonbio.com/20250630/taxonomy/role/DisclosureNetLossPerShareTables Net Loss Per Share (Tables) Tables http://annexonbio.com/20250630/taxonomy/role/DisclosureNetLossPerShare1 25 false false R26.htm 995655 - Disclosure - Segment Reporting (Tables) Sheet http://annexonbio.com/20250630/taxonomy/role/DisclosureSegmentReportingTables Segment Reporting (Tables) Tables http://annexonbio.com/20250630/taxonomy/role/DisclosureSegmentReporting 26 false false R27.htm 995665 - Disclosure - Organization - Additional Information (Details) Sheet http://annexonbio.com/20250630/taxonomy/role/DisclosureOrganizationAdditionalInformationDetails Organization - Additional Information (Details) Details 27 false false R28.htm 995675 - Disclosure - Basis of Presentation and Significant Accounting Policies - Additional Information (Details) Sheet http://annexonbio.com/20250630/taxonomy/role/DisclosureBasisOfPresentationAndSignificantAccountingPoliciesAdditionalInformationDetails Basis of Presentation and Significant Accounting Policies - Additional Information (Details) Details 28 false false R29.htm 995685 - Disclosure - Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on a Recurring Basis (Details) Sheet http://annexonbio.com/20250630/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfFinancialAssetsMeasuredAtFairValueOnARecurringBasisDetails Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on a Recurring Basis (Details) Details 29 false false R30.htm 995695 - Disclosure - Fair Value Measurements - Additional Information (Details) Sheet http://annexonbio.com/20250630/taxonomy/role/DisclosureFairValueMeasurementsAdditionalInformationDetails Fair Value Measurements - Additional Information (Details) Details 30 false false R31.htm 995705 - Disclosure - Balance Sheet Components - Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) Sheet http://annexonbio.com/20250630/taxonomy/role/DisclosureBalanceSheetComponentsScheduleOfReconciliationOfCashCashEquivalentsAndRestrictedCashDetails Balance Sheet Components - Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) Details 31 false false R32.htm 995715 - Disclosure - Balance Sheet Components - Summary of Prepaid Expenses and Other Current Assets (Details) Sheet http://annexonbio.com/20250630/taxonomy/role/DisclosureBalanceSheetComponentsSummaryOfPrepaidExpensesAndOtherCurrentAssetsDetails Balance Sheet Components - Summary of Prepaid Expenses and Other Current Assets (Details) Details 32 false false R33.htm 995735 - Disclosure - Balance Sheet Components - Summary of Property and Equipment, Net (Details) Sheet http://annexonbio.com/20250630/taxonomy/role/DisclosureBalanceSheetComponentsSummaryOfPropertyAndEquipmentNetDetails Balance Sheet Components - Summary of Property and Equipment, Net (Details) Details 33 false false R34.htm 995745 - Disclosure - Balance Sheet Components - Additional Information (Details) Sheet http://annexonbio.com/20250630/taxonomy/role/DisclosureBalanceSheetComponentsAdditionalInformationDetails Balance Sheet Components - Additional Information (Details) Details 34 false false R35.htm 995755 - Disclosure - Balance Sheet Components - Summary of Accrued and Other Current Liabilities (Details) Sheet http://annexonbio.com/20250630/taxonomy/role/DisclosureBalanceSheetComponentsSummaryOfAccruedAndOtherCurrentLiabilitiesDetails Balance Sheet Components - Summary of Accrued and Other Current Liabilities (Details) Details 35 false false R36.htm 995765 - Disclosure - Commitments and Contingencies - Additional Information (Details) Sheet http://annexonbio.com/20250630/taxonomy/role/DisclosureCommitmentsAndContingenciesAdditionalInformationDetails Commitments and Contingencies - Additional Information (Details) Details 36 false false R37.htm 995775 - Disclosure - Commitments and Contingencies - Future Minimum Lease Payments and Related Lease Liabilities (Details) Sheet http://annexonbio.com/20250630/taxonomy/role/DisclosureCommitmentsAndContingenciesFutureMinimumLeasePaymentsAndRelatedLeaseLiabilitiesDetails Commitments and Contingencies - Future Minimum Lease Payments and Related Lease Liabilities (Details) Details 37 false false R38.htm 995785 - Disclosure - Stockholders' Equity - Additional Information (Details) Sheet http://annexonbio.com/20250630/taxonomy/role/DisclosureStockholdersEquityAdditionalInformationDetails Stockholders' Equity - Additional Information (Details) Details 38 false false R39.htm 995795 - Disclosure - Stockholders' Equity - Summary of Warrants Activity (Details) Sheet http://annexonbio.com/20250630/taxonomy/role/DisclosureStockholdersEquitySummaryOfWarrantsActivityDetails Stockholders' Equity - Summary of Warrants Activity (Details) Details 39 false false R40.htm 995805 - Disclosure - Stockholders' Equity - Schedule of Common Stock Reserved for Future Issuance (Details) Sheet http://annexonbio.com/20250630/taxonomy/role/DisclosureStockholdersEquityScheduleOfCommonStockReservedForFutureIssuanceDetails Stockholders' Equity - Schedule of Common Stock Reserved for Future Issuance (Details) Details 40 false false R41.htm 995815 - Disclosure - Equity Incentive Plans - Additional Information (Details) Sheet http://annexonbio.com/20250630/taxonomy/role/DisclosureEquityIncentivePlansAdditionalInformationDetails Equity Incentive Plans - Additional Information (Details) Details 41 false false R42.htm 995825 - Disclosure - Equity Incentive Plans - Summary of Stock Option Activity (Details) Sheet http://annexonbio.com/20250630/taxonomy/role/DisclosureEquityIncentivePlansSummaryOfStockOptionActivityDetails Equity Incentive Plans - Summary of Stock Option Activity (Details) Details 42 false false R43.htm 995835 - Disclosure - Equity Incentive Plans - Summary of RSU Activity under Equity Incentive Plan (Details) Sheet http://annexonbio.com/20250630/taxonomy/role/DisclosureEquityIncentivePlansSummaryOfRsuActivityUnderEquityIncentivePlanDetails Equity Incentive Plans - Summary of RSU Activity under Equity Incentive Plan (Details) Details 43 false false R44.htm 995845 - Disclosure - Equity Incentive Plans - Summary of Stock-Based Compensation Expense (Details) Sheet http://annexonbio.com/20250630/taxonomy/role/DisclosureEquityIncentivePlansSummaryOfStockbasedCompensationExpenseDetails Equity Incentive Plans - Summary of Stock-Based Compensation Expense (Details) Details 44 false false R45.htm 995855 - Disclosure - Equity Incentive Plans - Summary of Fair Value of Each Stock Option Issued Estimated on the Date of Grant Using the Black-Scholes Option Pricing Model (Details) Sheet http://annexonbio.com/20250630/taxonomy/role/DisclosureEquityIncentivePlansSummaryOfFairValueOfEachStockOptionIssuedEstimatedOnTheDateOfGrantUsingTheBlackscholesOptionPricingModel Equity Incentive Plans - Summary of Fair Value of Each Stock Option Issued Estimated on the Date of Grant Using the Black-Scholes Option Pricing Model (Details) Details 45 false false R46.htm 995865 - Disclosure - Net Loss Per Share - Additional Information (Details) Sheet http://annexonbio.com/20250630/taxonomy/role/DisclosureNetLossPerShareAdditionalInformationDetails Net Loss Per Share - Additional Information (Details) Details 46 false false R47.htm 995875 - Disclosure - Net Loss Per Share - Summary of Outstanding Potentially Dilutive Shares Excluded From Calculation of Diluted Net Loss Per Share (Details) Sheet http://annexonbio.com/20250630/taxonomy/role/DisclosureNetLossPerShareSummaryOfOutstandingPotentiallyDilutiveSharesExcludedFromCalculationOfDilutedNetLossPerShareDetails Net Loss Per Share - Summary of Outstanding Potentially Dilutive Shares Excluded From Calculation of Diluted Net Loss Per Share (Details) Details 47 false false R48.htm 995885 - Disclosure - Segment Reporting- Additional Information (Details) Sheet http://annexonbio.com/20250630/taxonomy/role/DisclosureSegmentReportingAdditionalInformationDetails Segment Reporting- Additional Information (Details) Details 48 false false R49.htm 995895 - Disclosure - Segment Reporting - Schedule of Operations forReportable Segment (Details) Sheet http://annexonbio.com/20250630/taxonomy/role/DisclosureSegmentReportingScheduleOfOperationsForreportableSegmentDetails Segment Reporting - Schedule of Operations forReportable Segment (Details) Details 49 false false All Reports Book All Reports annx-20250630.htm annx-20250630.xsd http://fasb.org/us-gaap/2024 http://xbrl.sec.gov/dei/2024 http://xbrl.sec.gov/ecd/2024 false false