Organization and Basis of Presentation	9 Months Ended
Organization and Basis of Presentation	Sep. 30, 2025
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Basis of Presentation	Organization and Basis of Presentation Adverum Biotechnologies, Inc. (the “Company” or “Adverum”) was incorporated in Delaware on July 17, 2006 and is headquartered in Redwood City, California. The Company aims to establish gene therapy as a new standard of care for highly prevalent ocular diseases. The Company develops gene therapy product candidates intended to provide durable efficacy by inducing sustained expression of a therapeutic protein. For information regarding the Agreement and Plan of Merger ("Merger Agreement") and Secured Promissory Note ("Secured Note") with Eli Lilly and Company, an Indiana corporation (“Lilly”), dated October 24, 2025, see Note 9 “Subsequent Events”. Going Concern, Liquidity, Risks and Uncertainties—As of September 30, 2025, the Company has devoted substantially all of its efforts to product development and has not realized product sales revenues from its planned principal operations. The Company has a limited operating history, and the sales and income potential of the Company’s business and market are unproven. The Company has experienced net losses since its inception and, as of September 30, 2025, had an accumulated deficit of $1.2 billion. The Company used $109.7 million of cash in operations during the nine months ended September 30, 2025. The Company expects to continue to incur net losses and operating cash outflows for at least the next several years. A successful transition to attaining profitable operations is dependent upon achieving a level of revenue adequate to support the Company’s cost structure. As of September 30, 2025, the Company had cash, cash equivalents and short-term investments of $26.1 million. The Company has determined that its cash and cash equivalents as of September 30, 2025, would be insufficient to fund its operations for a period of at least twelve months from the date these unaudited condensed consolidated financial statements are issued, which raises substantial doubt regarding the Company’s ability to continue as a going concern. The Company expects its cash, cash equivalents, and advances under the Secured Note with Lilly to fund operations through the anticipated consummation of the merger. See Note 9 “Subsequent Events” for more information. If the merger is not completed as anticipated, the Company will require additional financing to fund its operations. If the Merger Agreement is terminated, Lilly may accelerate the obligations under the Secured Note. If the Company is unable to obtain additional financing when needed and on acceptable terms, Lilly, as the secured creditor under the Secured Note, may exercise its rights and remedies, including foreclosing on the Company’s assets. The Company’s financial statements have been prepared using the going concern basis of accounting, which contemplates the continuity of operations, realization of assets and the satisfaction of liabilities and commitments in the ordinary course of business. The financial statements do not include any adjustments relating to the recoverability and classification of recorded asset amounts or the amounts and classification of liabilities that might result from the outcome of the uncertainties described above. Basis of Presentation — The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) and follow the requirements of the Securities and Exchange Commission (“SEC”) for interim reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by U.S. GAAP can be condensed or omitted. These unaudited condensed consolidated financial statements have been prepared on the same basis as the Company’s annual consolidated 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 consolidated financial information. The condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The results of operations for the three and nine months ended September 30, 2025 are not necessarily indicative of the results to be expected for the full year or any other future period. The balance sheet as of December 31, 2024 is derived from the audited consolidated financial statements at that date but does not include all of the information required by U.S. GAAP for complete consolidated financial statements. The accompanying unaudited condensed consolidated financial statements and related financial information should be read in conjunction with the audited consolidated financial statements and the related notes thereto included in the Company’s Annual Report on Form 10-K, filed with the SEC on April 15, 2025 for the year ended December 31, 2024.