Description of Business and Basis of Presentation	3 Months Ended
Mar. 31, 2026
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business and Basis of Presentation	1. Description of Business and Basis of Presentation Description of Business—Lexeo Therapeutics, Inc. (the “Company”) is a clinical stage genetic medicine company dedicated to pioneering novel treatments for cardiovascular disease. The Company utilizes adeno-associated viruses (“AAV”) that have been engineered to transfer genes to patients. The Company’s therapeutic investigational treatments include AAV-based gene therapies primarily in the clinical and late pre-clinical stages of research and development. The Company is located in New York, NY and was first formed on February 17, 2017, as an LLC under the laws of the State of Delaware under the legal name Lexeo Therapeutics, LLC. The Company filed and executed a certificate of conversion to a corporation on November 20, 2020, to convert the LLC to Lexeo Therapeutics, Inc., a Delaware corporation. All of the Company’s tangible assets are held in the United States (“U.S.”). Basis of Presentation and Principles of Consolidation—The Company’s fiscal year ends on December 31, and its fiscal quarters end on March 31, June 30, and September 30. These unaudited condensed financial statements and these notes reflect the operations of the Company have been prepared in conformity with generally accepted accounting principles in the United States of America (“GAAP”) for interim financial information. Accordingly, they do not include all of the information and disclosures required by GAAP for complete financial statements. These unaudited condensed financial statements and accompanying notes should be read in conjunction with the Company’s audited financial statements and notes thereto for the year ended December 31, 2025 (the “Annual Financial Statements”) included in the Company's Annual Report on Form 10-K, filed with the United States Securities and Exchange Commission on March 30, 2026. The unaudited condensed balance sheet at December 31, 2025 has been derived from the audited financial statements at that date. In the opinion of management, all adjustments (consisting of normal recurring adjustments) considered necessary to present fairly the financial position of the Company and its results of operations and cash flows for the periods presented have been included. Operating results for the three months ended March 31, 2026 are not necessarily indicative of the results that may be expected for the year ending December 31, 2026, for any other interim period, or for any other future year. Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASU”) of the Financial Accounting Standards Board (“FASB”). The Company has no unconsolidated subsidiaries. Certain prior period balances have been reclassified to conform to the current period presentation. Need for Additional Capital—Since inception, the Company has incurred net losses and negative cash flows from operations, including net losses of $20.2 million and $100.0 million during the three months ended March 31, 2026 and the year ended December 31, 2025, respectively. As of March 31, 2026, the Company had cash, cash equivalents, and investments in U.S. Treasury Securities of $227.6 million and an accumulated deficit of $400.3 million and expects to incur substantial operating losses and negative cash flows from operations for the foreseeable future. During the year ended December 31, 2025, the Company received total net proceeds of approximately $73.1 million after deducting approximately $6.9 million of commissions and offering expenses in the May 2025 Private Placement (as defined below) (see Note 8), as well as net proceeds of approximately $143.9 million after deducting approximately $9.8 million of underwriter commissions, placement agent fees and estimated offering expenses in the October 2025 Financing Transactions (as defined below) (see Note 8). In April 2026, the Company sold 4,424,778 shares of its common stock under the ATM Program pursuant to the Sales Agreement with Leerink (each as defined below) at a volume-weighted average price of $5.65 per share, and received gross and net proceeds of $25.0 million and approximately $23.6 million, respectively, after deducting approximately $0.8 million of fees paid to Leerink and $0.6 million of other third-party offering costs (see Note 8 and Note 14). Management estimates that the Company's current cash, cash equivalents, and investments in U.S. Treasury securities balances are sufficient to fund its operations for at least 12 months from the issuance date of these financial statements. If the Company is unable to obtain additional funding before achieving sufficient profitability and positive cash flows from operations, if ever, the Company will be forced to delay, reduce or eliminate some or all of its research and development programs, which could adversely affect its business prospects, or the Company may be unable to continue operations. Although management continues to pursue plans to obtain additional funding before achieving sufficient profitability and positive cash flows from operations, there is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations, if at all. Risks and Uncertainties—The Company is subject to risks and uncertainties common to early-stage companies in the biopharmaceutical industry, including, but not limited to, successful discovery and development of its product candidates, development by competitors of new technological innovations, dependence on key personnel, the ability to attract and retain qualified employees, protection of proprietary technology, compliance with governmental regulations, the ability to secure additional capital to fund operations, and commercial success of its product candidates. Any of the Company’s current product candidates and future product candidates that it may develop will require extensive non-clinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel, infrastructure, and extensive compliance- reporting capabilities. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales.

Description of Business and Basis of Presentation

3 Months Ended

Mar. 31, 2026

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Description of Business and Basis of Presentation

1. Description of Business and Basis of Presentation

Description of Business—Lexeo Therapeutics, Inc. (the “Company”) is a clinical stage genetic medicine company dedicated to pioneering novel treatments for cardiovascular disease. The Company utilizes adeno-associated viruses (“AAV”) that have been engineered to transfer genes to patients. The Company’s therapeutic investigational treatments include AAV-based gene therapies primarily in the clinical and late pre-clinical stages of research and development.

The Company is located in New York, NY and was first formed on February 17, 2017, as an LLC under the laws of the State of Delaware under the legal name Lexeo Therapeutics, LLC. The Company filed and executed a certificate of conversion to a corporation on November 20, 2020, to convert the LLC to Lexeo Therapeutics, Inc., a Delaware corporation. All of the Company’s tangible assets are held in the United States (“U.S.”).

Basis of Presentation and Principles of Consolidation—The Company’s fiscal year ends on December 31, and its fiscal quarters end on March 31, June 30, and September 30.

These unaudited condensed financial statements and these notes reflect the operations of the Company have been prepared in conformity with generally accepted accounting principles in the United States of America (“GAAP”) for interim financial information. Accordingly, they do not include all of the information and disclosures required by GAAP for complete financial statements. These unaudited condensed financial statements and accompanying notes should be read in conjunction with the Company’s audited financial statements and notes thereto for the year ended December 31, 2025 (the “Annual Financial Statements”) included in the Company's Annual Report on Form 10-K, filed with the United States Securities and Exchange Commission on March 30, 2026. The unaudited condensed balance sheet at December 31, 2025 has been derived from the audited financial statements at that date. In the opinion of management, all adjustments (consisting of normal recurring adjustments) considered necessary to present fairly the financial position of the Company and its results of operations and cash flows for the periods presented have been included. Operating results for the three months ended March 31, 2026 are not necessarily indicative of the results that may be expected for the year ending December 31, 2026, for any other interim period, or for any other future year.

Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASU”) of the Financial Accounting Standards Board (“FASB”). The Company has no unconsolidated subsidiaries. Certain prior period balances have been reclassified to conform to the current period presentation.

Need for Additional Capital—Since inception, the Company has incurred net losses and negative cash flows from operations, including net losses of $20.2 million and $100.0 million during the three months ended March 31, 2026 and the year ended December 31, 2025, respectively. As of March 31, 2026, the Company had cash, cash equivalents, and investments in U.S. Treasury Securities of $227.6 million and an accumulated deficit of $400.3 million and expects to incur substantial operating losses and negative cash flows from operations for the foreseeable future. During the year ended December 31, 2025, the Company received total net proceeds of approximately $73.1 million after deducting approximately $6.9 million of commissions and offering expenses in the May 2025 Private Placement (as defined below) (see Note 8), as well as net proceeds of approximately $143.9 million after deducting approximately $9.8 million of underwriter commissions, placement agent fees and estimated offering expenses in the October 2025 Financing Transactions (as defined below) (see Note 8). In April 2026, the Company sold 4,424,778 shares of its common stock under the ATM Program pursuant to the Sales Agreement with Leerink (each as defined below) at a volume-weighted average price of $5.65 per share, and received gross and net proceeds of $25.0 million and approximately $23.6 million, respectively, after deducting approximately $0.8 million of fees paid to Leerink and $0.6 million of other third-party offering costs (see Note 8 and Note 14). Management estimates that the Company's current cash, cash equivalents, and investments in U.S. Treasury securities balances are sufficient to fund its operations for at least 12 months from the issuance date of these financial statements.

If the Company is unable to obtain additional funding before achieving sufficient profitability and positive cash flows from operations, if ever, the Company will be forced to delay, reduce or eliminate some or all of its research and development programs, which could adversely affect its business prospects, or the Company may be unable to continue operations. Although management continues to pursue plans to obtain additional funding before achieving sufficient profitability and positive cash flows from operations, there is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations, if at all.

Risks and Uncertainties—The Company is subject to risks and uncertainties common to early-stage companies in the biopharmaceutical industry, including, but not limited to, successful discovery and development of its product candidates, development by competitors of new technological innovations, dependence on key personnel, the ability to attract and retain qualified employees, protection of proprietary technology, compliance with governmental regulations, the ability to secure additional capital to fund operations, and commercial success of its product candidates. Any of the Company’s current product candidates and future product candidates that it may develop will require extensive non-clinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel, infrastructure, and extensive compliance- reporting capabilities. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales.