Lexeo Therapeutics, Inc.

ATM Offering

On March 24, 2025, we entered into a Sales Agreement with Leerink Partners LLC, as the Sales Agent, pursuant to which we may, from time to time, sell up to an aggregate amount of $75.0 million of our common stock through the Sales Agent in an “at-the-market” offering, or the ATM Offering. We will pay the Sales Agent a commission equal to 3% of the aggregate gross proceeds we receive from all sales of our common stock under the Sales Agreement. We have also provided the Sales Agent with customary indemnification rights. The Sales Agreement remains in effect until the earlier of selling all shares available under the Sales Agreement or until such agreement is terminated by written notice from either of the parties pursuant to the terms thereof. We are not obligated to make any sales of our common stock under the Sales Agreement, and no sales have been made under the Sales Agreement as of the filing of this Annual Report.

The ATM Offering is being made under a prospectus supplement to be dated March 24, 2025 and filed with the Securities and Exchange Commission on March 24, 2025, and the related prospectus contained in our shelf registration statement on Form S-3 (Registration No. 333- 283781) filed on December 13, 2024, and declared effective by the Securities and Exchange Commission on December 19, 2024.

A copy of the Sales Agreement is filed as Exhibit 10.32 to this Annual Report. The foregoing description of the Sales Agreement does not purport to be complete and is qualified in its entirety by reference to Exhibit 10.32. A copy of the opinion of Wilson Sonsini Goodrich & Rosati, P.C. relating to the validity of the securities issued in the ATM Offering is filed as Exhibit 5.1 to this Annual Report.

Securities Trading Plans of Directors and Executive Officers

No officers, as defined in Rule 16a-1(f), or directors adopted or terminated a “Rule 10b5-1 trading arrangement” or a “non-Rule 10b5-1 trading arrangement,” as defined in Regulation S-K Item 408, during the last fiscal quarter.