Summary of Significant Accounting Policies (Policies)	6 Months Ended
Jun. 30, 2026
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The Company’s unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) for interim financial information and pursuant to applicable rules and regulations of the SEC regarding interim financial reporting. Accordingly, they do not include all of the information and notes required by U.S. GAAP for complete consolidated financial statements. These unaudited condensed consolidated financial statements include only normal and recurring adjustments, which are normal in nature, that the Company believes are necessary to a fair statement of the Company’s financial position and the results of its operations and cash flows. These unaudited interim condensed consolidated financial statements have been prepared on the same basis as the Company’s annual financial statements and, in the opinion of management, reflect all adjustments, consisting only of normal recurring adjustments which are necessary for a fair statement of the Company’s financial information. The balance sheet as of December 31, 2025 was derived from the audited financial statements as of that date. The financial statements for the fiscal three and six months ended June 30, 2026 and 2025 are consolidated and include the accounts of the Company and its subsidiary. Certain reclassifications on the condensed consolidated statements of operations and comprehensive loss have been made to prior period amounts to conform to current period presentation. These interim financial results are not necessarily indicative of results to be expected for the full year or any other period. These unaudited condensed consolidated financial statements and the notes accompanying them should be read in conjunction with the Company’s Annual Report on Form 10-K for the year ended December 31, 2025.
Consolidation	Consolidation The accompanying unaudited condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiary, Bolt Biotherapeutics Australia PTY LTD (which are referred to herein, collectively, as the Company where context requires). Bolt Biotherapeutics Australia PTY LTD did not hold any assets or generate revenue during and as of the three and six months ended June 30, 2026 and 2025. All intercompany balances and transactions have been eliminated on consolidation.
Risks and Uncertainties	Risks and Uncertainties The Company is subject to a number of risks similar to other early-stage biopharmaceutical companies, including, but not limited to, changes in any of the following areas that the Company believes could have a material adverse effect on its future financial position or results of operations: risks related to the successful discovery and development of its product candidates, ability to raise additional capital, development of new technological innovations by its competitors, delay or inability to obtain chemical or biological intermediates from such suppliers required for the synthesis of the Company’s product candidates, protection of intellectual property rights, litigation or claims against the Company based on intellectual property rights, and regulatory clearance and market acceptance of the Company’s products. Global economic and business activities continue to face widespread macroeconomic uncertainties, including pandemics, labor shortages, inflation and monetary supply shifts, recession risks and potential disruptions from major geopolitical conflicts. The Company continues to actively monitor the impact of these macroeconomic factors on its financial condition, liquidity, operations, and workforce. The extent of the impact of these factors on the Company’s operational and financial performance, including its ability to execute its business strategies and initiatives in the expected time frame, will depend on future developments, which are uncertain and cannot be predicted; however, any continued or renewed disruption resulting from these factors could negatively impact the Company’s business. The Company relies on single source manufacturers and suppliers for the supply of its product candidates. Disruption from these manufacturers or suppliers would have a negative impact on the Company’s business, financial position, and results of operations.
Liquidity and Going Concern	Liquidity and Going Concern The Company has incurred net losses and negative cash flows from operations since its inception, has an accumulated deficit $475.7 million and anticipates continuing to incur net losses for the foreseeable future. Under the Company's current plan, management believes its cash and cash equivalents and marketable securities of $18.1 million as of June 30, 2026 will not be sufficient for the Company to continue as a going concern for at least one year from the issuance date of these financial statements. The Company believes that this raises substantial doubt about its ability to continue as a going concern within one year after the issuance of the unaudited condensed consolidated financial statements. As a result, the Company will be required to raise additional capital by partnering, selling equity, or other means. There can be no assurance as to whether partnering efforts will be successful or whether additional financing will be available on terms acceptable to the Company, if at all. If sufficient funds on acceptable terms are not available when needed, it would have a negative impact on the Company’s financial condition and could force the Company to delay, limit, reduce, or terminate product development or future commercialization efforts or grant rights to develop and market product candidates that the Company would otherwise plan to develop and market itself. The accompanying unaudited condensed consolidated financial statements have been prepared assuming that the Company will continue as a going concern, which contemplates the realization of assets and the settlement of liabilities and commitments in the normal course of business. The accompanying unaudited condensed consolidated financial statements do not reflect any adjustments relating to the recoverability and reclassifications of assets and liabilities that might be necessary if the Company is unable to continue as a going concern. The Company will need to raise additional capital to continue the advancement of its programs. In the near term, the Company's primary uses of cash will be to fund the completion of key milestones for clinical programs and to fund its operations, including research and development activities and employee salaries. This includes significant costs relating to clinical trials and manufacture of the Company's product candidates. The Company's uses of cash in the long term will be similar as the Company advances its research and development activities and pays employee salaries. Most pharmaceutical products require larger clinical trials as development progresses, and the Company expects its funding requirements to grow with the advancement of its programs. The Company's long-term funding requirements will depend on many factors, which are uncertain but include its portfolio prioritization decisions and the success of its collaborations. In turn, the Company's ability to raise additional capital through equity or partnering will depend on the general economic environment in which it operates and its ability to achieve key milestones.
Reverse Stock Split	Reverse Stock Split On June 6, 2025, the Company effected a 1-for-20 reverse stock split (the “Reverse Stock Split”) of its common stock. The par value per share and the number of authorized shares were not adjusted as a result of the Reverse Stock Split. The shares of common stock underlying outstanding stock options were proportionately reduced and the respective exercise prices, if applicable, were proportionately increased in accordance with the terms of the agreements governing such stock. In addition, the shares available for grants under the Company’s equity incentive plans and employee stock purchase plan were adjusted as a result of the Reverse Stock Split. All references to common stock, options to purchase common stock, common stock share data, per share data, and related information contained in the unaudited condensed consolidated financial statements have been retrospectively adjusted to reflect the effect of the Reverse Stock Split for all periods presented.
Use of Estimates	Use of Estimates The preparation of the unaudited condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, and the disclosure of contingent assets and liabilities at the date of the unaudited condensed consolidated financial statements and the reported amounts of expenses during the reporting period. On an ongoing basis, the Company evaluates its estimates and assumptions, including those related to revenue recognition, stock-based compensation, restructuring costs, long-lived assets impairment assessment, and accrued liabilities. Management bases its estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Actual results may differ materially from those estimates.
Reclassification	Reclassification Certain amounts in the accompanying unaudited condensed consolidated financial statements were reclassified to conform to the current presentation.
Long-lived Assets Impairment Assessment	Long-lived Assets Impairment Assessment Long-lived assets, including operating lease assets, are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. The recoverability of assets to be held and used is measured by a comparison of the carrying amount of the asset group to future net cash flows estimated by the Company to be generated by such assets. If such asset group is considered to be impaired, the impairment to be recognized is the amount by which the carrying amount of the asset group exceeds the fair value of the asset group. Any impairment loss is allocated to the long-lived assets of the group on a pro rata basis using the relative carrying amounts of those assets, except that the carrying amount of an individual asset cannot be reduced below its fair value. Factors that may indicate potential impairment and trigger an impairment test include, but are not limited to, general macroeconomic conditions, conditions specific to the industry and market, an adverse change in legal factors and business climate or operational performance of the business. Calculating the fair value of a reporting unit, an asset group and an individual asset involves significant estimates and assumptions. These estimates and assumptions include, among others, projected future cash flows, risk-adjusted discount rates, future economic and market conditions, and the determination of appropriate market comparables. Changes in these factors and assumptions used can materially affect the amount of impairment loss recognized in the period the asset was considered impaired.
Allowance for Credit Losses	Allowance for Credit Losses For available-for-sale securities in an unrealized loss position, the Company first assesses whether it intends to sell, or if it is more likely than not that the Company will be required to sell, the security before recovery of its amortized cost basis. If either of the criteria regarding intent or requirement to sell is met, the security’s amortized cost basis is written down to fair value through earnings. For available-for-sale securities that do not meet the aforementioned criteria, the Company evaluates whether the decline in fair value has resulted from credit losses or other factors. In making this assessment, the Company considers the severity of the impairment, any changes in interest rates, market conditions, changes to the underlying credit ratings and forecasted recovery, among other factors. The credit-related portion of unrealized losses, and any subsequent improvements, are recorded in interest income through an allowance account. Any impairment that has not been recorded through an allowance for credit losses is included in other comprehensive income (loss) on the statements of operations and comprehensive loss. The Company elected the practical expedient to exclude the applicable accrued interest from both the fair value and amortized costs basis of its available-for-sale securities for purposes of identifying and measuring an impairment. Accrued interest receivable on available-for-sale securities is recorded within cash and cash equivalents on the Company's balance sheets. The Company's accounting policy is to not measure an allowance for credit loss for accrued interest receivable and to write-off any uncollectible accrued interest receivable as a reversal of interest income in a timely manner, which the Company considers to be in the period in which it determines the accrued interest will not be collected by the Company.
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments that potentially subject the Company to concentration of credit risk consist of cash, cash equivalents and marketable securities. As of June 30, 2026 and December 31, 2025, most of the Company’s funds were invested with a registered investment manager and custodied at one financial institution, with operating cash kept at a separate financial institution, and account balances may at times exceed federally insured limits. Management believes that the Company is not subject to unusual or significant credit risk beyond the normal credit risk associated with commercial banking relationships.
Net Loss Per Share	Net Loss Per Share Basic net loss per share is calculated by dividing the net loss by the weighted-average number of shares of common stock outstanding during the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss by the weighted-average number of common stock and potentially dilutive securities outstanding for the period. For purposes of the diluted net loss per share calculation, stock options, common stock subject to repurchase related to unvested restricted stock awards and early exercise of stock options are considered potentially dilutive securities. Basic and diluted net loss per share is presented in conformity with the two-class method required for participating securities. The Company considers the shares issued upon the early exercise of stock options subject to repurchase to be participating securities because holders of such shares have non-forfeitable dividend rights in the event a dividend is paid on common stock. The holders of early exercised shares subject to repurchase do not have a contractual obligation to share in the Company’s losses. As such, the net loss was attributed entirely to common stockholders. Because the Company has reported a net loss for all periods presented, diluted net loss per share is the same as basic net loss per share for all periods presented as potentially dilutive securities were anti-dilutive.
Recent Accounting Standards	Recent Accounting Standards From time to time, new accounting standards are issued by the Financial Accounting Standards Board (the “FASB”), or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the impact of recently issued standards that are not yet effective will not have a material impact on the Company’s financial position or results of operations upon adoption. In November 2024, the FASB issued ASU 2024-03, Income Statement - Reporting Comprehensive Income - Expense Disaggregation Disclosures (Subtopic 220-40), which is intended to enhance transparency into the nature and function of expenses, primarily through additional disclosures on certain cost and expenses. ASU 2024-03 should be applied on a prospective basis, and retrospective application is permitted. ASU 2024-03 is effective for annual periods beginning after December 15, 2026, and interim reporting periods beginning after December 15, 2027. Early adoption is permitted. The Company is currently evaluating the impact of this guidance. In May 2025, the FASB issued ASU 2025-04, Revenue from Contracts with Customers (Topic 606) and Compensation—Stock Compensation (Topic 718): Share-Based Consideration Payable to a Customer, to clarify the accounting treatment for equity instruments granted to customers. The guidance is effective for fiscal years beginning after December 15, 2026, and interim periods within those fiscal years. Early adoption is permitted. The Company is currently evaluating the impact of this standard on its financial statements and related disclosures; at this time it does not expect it to materially affect its unaudited condensed consolidated financial statements.

Summary of Significant Accounting Policies (Policies)

6 Months Ended

Jun. 30, 2026

The Company’s unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) for interim financial information and pursuant to applicable rules and regulations of the SEC regarding interim financial reporting. Accordingly, they do not include all of the information and notes required by U.S. GAAP for complete consolidated financial statements. These unaudited condensed consolidated financial statements include only normal and recurring adjustments, which are normal in nature, that the Company believes are necessary to a fair statement of the Company’s financial position and the results of its operations and cash flows. These unaudited interim condensed consolidated financial statements have been prepared on the same basis as the Company’s annual financial statements and, in the opinion of management, reflect all adjustments, consisting only of normal recurring adjustments which are necessary for a fair statement of the Company’s financial information. The balance sheet as of December 31, 2025 was derived from the audited financial statements as of that date. The financial statements for the fiscal three and six months ended June 30, 2026 and 2025 are consolidated and include the accounts of the Company and its subsidiary. Certain reclassifications on the condensed consolidated statements of operations and comprehensive loss have been made to prior period amounts to conform to current period presentation. These interim financial results are not necessarily indicative of results to be expected for the full year or any other period. These unaudited condensed consolidated financial statements and the notes accompanying them should be read in conjunction with the Company’s Annual Report on Form 10-K for the year ended December 31, 2025.

Consolidation

The accompanying unaudited condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiary, Bolt Biotherapeutics Australia PTY LTD (which are referred to herein, collectively, as the Company where context requires). Bolt Biotherapeutics Australia PTY LTD did not hold any assets or generate revenue during and as of the three and six months ended June 30, 2026 and 2025. All intercompany balances and transactions have been eliminated on consolidation.

Risks and Uncertainties

The Company is subject to a number of risks similar to other early-stage biopharmaceutical companies, including, but not limited to, changes in any of the following areas that the Company believes could have a material adverse effect on its future financial position or results of operations: risks related to the successful discovery and development of its product candidates, ability to raise additional capital, development of new technological innovations by its competitors, delay or inability to obtain chemical or biological intermediates from such suppliers required for the synthesis of the Company’s product candidates, protection of intellectual property rights, litigation or claims against the Company based on intellectual property rights, and regulatory clearance and market acceptance of the Company’s products.

Global economic and business activities continue to face widespread macroeconomic uncertainties, including pandemics, labor shortages, inflation and monetary supply shifts, recession risks and potential disruptions from major geopolitical conflicts. The Company continues to actively monitor the impact of these macroeconomic factors on its financial condition, liquidity, operations, and workforce. The extent of the impact of these factors on the Company’s operational and financial performance, including its ability to execute its business strategies and initiatives in the expected time frame, will depend on future developments, which are uncertain and cannot be predicted; however, any continued or renewed disruption resulting from these factors could negatively impact the Company’s business.

The Company relies on single source manufacturers and suppliers for the supply of its product candidates. Disruption from these manufacturers or suppliers would have a negative impact on the Company’s business, financial position, and results of operations.

Liquidity and Going Concern

The Company has incurred net losses and negative cash flows from operations since its inception, has an accumulated deficit $475.7 million and anticipates continuing to incur net losses for the foreseeable future. Under the Company's current plan, management believes its cash and cash equivalents and marketable securities of $18.1 million as of June 30, 2026 will not be sufficient for the Company to continue as a going concern for at least one year from the issuance date of these financial statements. The Company believes that this raises substantial doubt about its ability to continue as a going concern within one year after the issuance of the unaudited condensed consolidated financial statements.

As a result, the Company will be required to raise additional capital by partnering, selling equity, or other means. There can be no assurance as to whether partnering efforts will be successful or whether additional financing will be available on terms acceptable to the Company, if at all. If sufficient funds on acceptable terms are not available when needed, it would have a negative impact on the Company’s financial condition and could force the Company to delay, limit, reduce, or terminate product development or future commercialization efforts or grant rights to develop and market product candidates that the Company would otherwise plan to develop and market itself.

The accompanying unaudited condensed consolidated financial statements have been prepared assuming that the Company will continue as a going concern, which contemplates the realization of assets and the settlement of liabilities and commitments in the normal course of business. The accompanying unaudited condensed consolidated financial statements do not reflect any adjustments relating to the recoverability and reclassifications of assets and liabilities that might be necessary if the Company is unable to continue as a going concern.

The Company will need to raise additional capital to continue the advancement of its programs. In the near term, the Company's primary uses of cash will be to fund the completion of key milestones for clinical programs and to fund its operations, including research and development activities and employee salaries. This includes significant costs relating to clinical trials and manufacture of the Company's product candidates. The Company's uses of cash in the long term will be similar as the Company advances its research and development activities and pays employee salaries. Most pharmaceutical products require larger clinical trials as development progresses, and the Company expects its funding requirements to grow with the advancement of its programs. The Company's long-term funding requirements will depend on many factors, which are uncertain but include its portfolio prioritization decisions and the success of its collaborations. In turn, the Company's ability to raise additional capital through equity or partnering will depend on the general economic environment in which it operates and its ability to achieve key milestones.

Reverse Stock Split

On June 6, 2025, the Company effected a 1-for-20 reverse stock split (the “Reverse Stock Split”) of its common stock. The par value per share and the number of authorized shares were not adjusted as a result of the Reverse Stock Split. The shares of common stock underlying outstanding stock options were proportionately reduced and the respective exercise prices, if applicable, were proportionately increased in accordance with the terms of the agreements governing such stock. In addition, the shares available for grants under the Company’s equity incentive plans and employee stock purchase plan were adjusted as a result of the Reverse Stock Split. All references to common stock, options to purchase common stock, common stock share data, per share data, and related information contained in the unaudited condensed consolidated financial statements have been retrospectively adjusted to reflect the effect of the Reverse Stock Split for all periods presented.

Use of Estimates

The preparation of the unaudited condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, and the disclosure of contingent assets and liabilities at the date of the unaudited condensed consolidated financial statements and the reported amounts of expenses during the reporting period. On an ongoing basis, the Company evaluates its estimates and assumptions, including those related to revenue recognition, stock-based compensation, restructuring costs, long-lived assets impairment assessment, and accrued liabilities. Management bases its estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Actual results may differ materially from those estimates.

Reclassification

Certain amounts in the accompanying unaudited condensed consolidated financial statements were reclassified to conform to the current presentation.

Long-lived Assets Impairment Assessment

Long-lived assets, including operating lease assets, are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. The recoverability of assets to be held and used is measured by a comparison of the carrying amount of the asset group to future net cash flows estimated by the Company to be generated by such assets. If such asset group is considered to be impaired, the impairment to be recognized is the amount by which the carrying amount of the asset group exceeds the fair value of the asset group. Any impairment loss is allocated to the long-lived assets of the group on a pro rata basis using the relative carrying amounts of those assets, except that the carrying amount of an individual asset cannot be reduced below its fair value.

Factors that may indicate potential impairment and trigger an impairment test include, but are not limited to, general macroeconomic conditions, conditions specific to the industry and market, an adverse change in legal factors and business climate or operational performance of the business.

Calculating the fair value of a reporting unit, an asset group and an individual asset involves significant estimates and assumptions. These estimates and assumptions include, among others, projected future cash flows, risk-adjusted discount rates, future economic and market conditions, and the determination of appropriate market comparables. Changes in these factors and assumptions used can materially affect the amount of impairment loss recognized in the period the asset was considered impaired.

Allowance for Credit Losses

For available-for-sale securities in an unrealized loss position, the Company first assesses whether it intends to sell, or if it is more likely than not that the Company will be required to sell, the security before recovery of its amortized cost basis. If either of the criteria regarding intent or requirement to sell is met, the security’s amortized cost basis is written down to fair value through earnings. For available-for-sale securities that do not meet the aforementioned criteria, the Company evaluates whether the decline in fair value has resulted from credit losses or other factors. In making this assessment, the Company considers the severity of the impairment, any changes in interest rates, market conditions, changes to the underlying credit ratings and forecasted recovery, among other factors. The credit-related portion of unrealized losses, and any subsequent improvements, are recorded in interest income through an allowance account. Any impairment that has not been recorded through an allowance for credit losses is included in other comprehensive income (loss) on the statements of operations and comprehensive loss.

The Company elected the practical expedient to exclude the applicable accrued interest from both the fair value and amortized costs basis of its available-for-sale securities for purposes of identifying and measuring an impairment. Accrued interest receivable on available-for-sale securities is recorded within cash and cash equivalents on the Company's balance sheets. The Company's accounting policy is to not measure an allowance for credit loss for accrued interest receivable and to write-off any uncollectible accrued interest receivable as a reversal of interest income in a timely manner, which the Company considers to be in the period in which it determines the accrued interest will not be collected by the Company.

Concentrations of Credit Risk

Financial instruments that potentially subject the Company to concentration of credit risk consist of cash, cash equivalents and marketable securities. As of June 30, 2026 and December 31, 2025, most of the Company’s funds were invested with a registered investment manager and custodied at one financial institution, with operating cash kept at a separate financial institution, and account balances may at times exceed federally insured limits. Management believes that the Company is not subject to unusual or significant credit risk beyond the normal credit risk associated with commercial banking relationships.

Net Loss Per Share

Basic net loss per share is calculated by dividing the net loss by the weighted-average number of shares of common stock outstanding during the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss by the weighted-average number of common stock and potentially dilutive securities outstanding for the period. For purposes of the diluted net loss per share calculation, stock options, common stock subject to repurchase related to unvested restricted stock awards and early exercise of stock options are considered potentially dilutive securities. Basic and diluted net loss per share is presented in conformity with the two-class method required for participating securities. The Company considers the shares issued upon the early exercise of stock options subject to repurchase to be participating securities because holders of such shares have non-forfeitable dividend rights in the event a dividend is paid on common stock. The holders of early exercised shares subject to repurchase do not have a contractual obligation to share in the Company’s losses. As such, the net loss was attributed entirely to common stockholders. Because the Company has reported a net loss for all periods presented, diluted net loss per share is the same as basic net loss per share for all periods presented as potentially dilutive securities were anti-dilutive.

Recent Accounting Standards

From time to time, new accounting standards are issued by the Financial Accounting Standards Board (the “FASB”), or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the impact of recently issued standards that are not yet effective will not have a material impact on the Company’s financial position or results of operations upon adoption.

In November 2024, the FASB issued ASU 2024-03, Income Statement - Reporting Comprehensive Income - Expense Disaggregation Disclosures (Subtopic 220-40), which is intended to enhance transparency into the nature and function of expenses, primarily through additional disclosures on certain cost and expenses. ASU 2024-03 should be applied on a prospective basis, and retrospective application is permitted. ASU 2024-03 is effective for annual periods beginning after December 15, 2026, and interim reporting periods beginning after December 15, 2027. Early adoption is permitted. The Company is currently evaluating the impact of this guidance.

In May 2025, the FASB issued ASU 2025-04, Revenue from Contracts with Customers (Topic 606) and Compensation—Stock Compensation (Topic 718): Share-Based Consideration Payable to a Customer, to clarify the accounting treatment for equity instruments granted to customers. The guidance is effective for fiscal years beginning after December 15, 2026, and interim periods within those fiscal years. Early adoption is permitted. The Company is currently evaluating the impact of this standard on its financial statements and related disclosures; at this time it does not expect it to materially affect its unaudited condensed consolidated financial statements.