Summary of Significant Accounting Policies	9 Months Ended
Sep. 30, 2025
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Use of estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting periods. Significant estimates and assumptions reflected in these condensed consolidated financial statements include, but are not limited to, the measurement of proportional performance of the combined license and research services performance obligation of our collaboration agreement and to a lesser extent, our accrual of research and development expenses. We base our estimates on historical experience, known trends and other market-specific or other relevant factors that we believe to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates, as there are changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results may differ from those estimates or assumptions. Unaudited interim financial information The condensed consolidated balance sheet as of December 31, 2024 was derived from audited financial statements but does not include all disclosures required by GAAP. The accompanying unaudited financial statements as of September 30, 2025 and for the three and nine months ended September 30, 2025 and 2024 have been prepared by us pursuant to the rules and regulations of the Securities and Exchange Commission, or SEC, for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. These financial statements should be read in conjunction with our audited financial statements included in our Annual Report on Form 10-K that was most recently filed with the SEC, or our 2024 Annual Report. In the opinion of management, all adjustments, consisting only of normal recurring adjustments necessary for a fair presentation of our financial position as of September 30, 2025, the results of operations for the three and nine months ended September 30, 2025 and 2024, and cash flows for the nine months ended September 30, 2025 and 2024 have been made. The results of operations for the three and nine months ended September 30, 2025 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2025 or any other period. Our significant accounting policies are described in Note 2 of the Notes to Consolidated Financial Statements included in our 2024 Annual Report. Recently issued accounting pronouncements In December 2023, the FASB issued its final standard to improve income tax disclosures. This standard, issued as ASU 2023-09, requires public business entities to annually disclose specific categories in the rate reconciliation and provide additional information for reconciling items that meet a quantitative threshold. This update is effective for us as of and for the year ended December 31, 2025. We anticipate that the adoption of ASU 2023-09 will expand our income tax footnote disclosures, including a more detailed effective tax rate reconciliation. In November 2024, the FASB issued its final standard on expense disaggregation disclosures. This standard, issued as ASU 2024-03, requires public business entities to disclose, on an annual and interim basis, disaggregated information about certain income statement line items in a tabular format in the notes to the financial statements. This update is effective for annual periods beginning after December 15, 2026. We are currently evaluating the impact the guidance will have on our consolidated financial statements.

Summary of Significant Accounting Policies

9 Months Ended

Sep. 30, 2025

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Use of estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting periods. Significant estimates

and assumptions reflected in these condensed consolidated financial statements include, but are not limited to, the measurement of proportional performance of the combined license and research services performance obligation of our collaboration agreement and to a lesser extent, our accrual of research and development expenses. We base our estimates on historical experience, known trends and other market-specific or other relevant factors that we believe to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates, as there are changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results may differ from those estimates or assumptions.

Unaudited interim financial information

The condensed consolidated balance sheet as of December 31, 2024 was derived from audited financial statements but does not include all disclosures required by GAAP. The accompanying unaudited financial statements as of September 30, 2025 and for the three and nine months ended September 30, 2025 and 2024 have been prepared by us pursuant to the rules and regulations of the Securities and Exchange Commission, or SEC, for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. These financial statements should be read in conjunction with our audited financial statements included in our Annual Report on Form 10-K that was most recently filed with the SEC, or our 2024 Annual Report. In the opinion of management, all adjustments, consisting only of normal recurring adjustments necessary for a fair presentation of our financial position as of September 30, 2025, the results of operations for the three and nine months ended September 30, 2025 and 2024, and cash flows for the nine months ended September 30, 2025 and 2024 have been made. The results of operations for the three and nine months ended September 30, 2025 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2025 or any other period.

Our significant accounting policies are described in Note 2 of the Notes to Consolidated Financial Statements included in our 2024 Annual Report.

Recently issued accounting pronouncements

In December 2023, the FASB issued its final standard to improve income tax disclosures. This standard, issued as ASU 2023-09, requires public business entities to annually disclose specific categories in the rate reconciliation and provide additional information for reconciling items that meet a quantitative threshold. This update is effective for us as of and for the year ended December 31, 2025. We anticipate that the adoption of ASU 2023-09 will expand our income tax footnote disclosures, including a more detailed effective tax rate reconciliation.

In November 2024, the FASB issued its final standard on expense disaggregation disclosures. This standard, issued as ASU 2024-03, requires public business entities to disclose, on an annual and interim basis, disaggregated information about certain income statement line items in a tabular format in the notes to the financial statements. This update is effective for annual periods beginning after December 15, 2026. We are currently evaluating the impact the guidance will have on our consolidated financial statements.

Generation Bio Co. 10-Q