SCHEDULE 13G/A 0001104659-23-119530 0001423053 XXXXXXXX LIVE 2 Common Stock ($0.0001 par value) (the "Shares") 06/30/2025 0001907108 Lexeo Therapeutics, Inc. 52886X107 345 Park Avenue South, Floor 6 New York NY 10010 Rule 13d-1(c) Citadel Advisors LLC DE 0.00 5325269.00 0.00 5325269.00 5325269.00 N 9.6 IA HC OO The percentages reported in this Schedule 13G are based upon 55,718,516 Shares outstanding comprised of (i) 54,001,214 Shares outstanding as of June 2, 2025 (according to the issuer's registration statement on From S-3 as filed with the Securities and Exchange Commission on June 13, 2025), and (ii) 1,717,302 Shares issuable upon conversion of certain warrants held by affiliates of the reporting persons. Citadel Advisors Holdings LP DE 0.00 5325269.00 0.00 5325269.00 5325269.00 N 9.6 HC PN Citadel GP LLC DE 0.00 5325269.00 0.00 5325269.00 5325269.00 N 9.6 HC OO Citadel Securities LLC DE 0.00 8843.00 0.00 8843.00 8843.00 N 0.0 BD OO Citadel Securities Group LP DE 0.00 8843.00 0.00 8843.00 8843.00 N 0.0 HC PN Citadel Securities GP LLC DE 0.00 8843.00 0.00 8843.00 8843.00 N 0.0 HC OO Kenneth Griffin X1 0.00 5334112.00 0.00 5334112.00 5334112.00 N 9.6 HC IN Lexeo Therapeutics, Inc. 345 Park Avenue South, Floor 6, New York, NY, 10010 This Schedule 13G is being jointly filed by Citadel Advisors LLC ("Citadel Advisors"), Citadel Advisors Holdings LP ("CAH"), Citadel GP LLC ("CGP"), Citadel Securities LLC ("Citadel Securities"), Citadel Securities Group LP ("CALC4"), Citadel Securities GP LLC ("CSGP") and Mr. Kenneth Griffin (collectively with Citadel Advisors, CAH, CGP, Citadel Securities, CALC4 and CSGP, the "Reporting Persons") with respect to the Shares of the above-named issuer owned by Citadel Multi-Strategy Equities Master Fund Ltd., a Cayman Islands company ("CM"), Citadel CEMF Investments Ltd., a Cayman Islands limited company ("CCIL"), and Citadel Securities. Such owned Shares may include other instruments exercisable for or convertible into Shares. Citadel Advisors is the portfolio manager for CM and CCIL. CAH is the sole member of Citadel Advisors. CGP is the general partner of CAH. CALC4 is the non-member manager of Citadel Securities. CSGP is the general partner of CALC4. Mr. Griffin is the President and Chief Executive Officer of CGP, and owns a controlling interest in CGP and CSGP. The filing of this statement shall not be construed as an admission that any of the Reporting Persons is the beneficial owner of any securities covered by the statement other than the securities actually owned by such person (if any). The address of each of the Reporting Persons is 830 Brickell Plaza, Miami, Florida 33131. Each of Citadel Advisors, CGP, Citadel Securities and CSGP is organized as a limited liability company under the laws of the State of Delaware. Each of CALC4 and CAH is organized as a limited partnership under the laws of the State of Delaware. Mr. Griffin is a U.S. citizen. Y 1. Each of Citadel Advisors LLC, Citadel Advisors Holdings LP and Citadel GP LLC may be deemed to beneficially own 5,325,269 Shares. 2. Citadel Securities LLC may be deemed to beneficially own 8,843 Shares. 3. Each of Citadel Securities Group LP and Citadel Securities GP LLC may be deemed to beneficially own 8,843 Shares. 4. Mr. Griffin may be deemed to beneficially own 5,334,112 Shares. 1. The number of Shares that each of Citadel Advisors LLC, Citadel Advisors Holdings LP and Citadel GP LLC may be deemed to beneficially own constitutes 9.6% of the Shares outstanding. 2. The number of Shares that Citadel Securities LLC may be deemed to beneficially own constitutes 0.0% of the Shares outstanding. 3. The number of Shares that each of Citadel Securities Group LP and Citadel Securities GP LLC may be deemed to beneficially own constitutes 0.0% of the Shares outstanding. 4. The number of Shares that Mr. Griffin may be deemed to beneficially own constitutes 9.6% of the Shares outstanding. 1. Each of Citadel Advisors LLC, Citadel Advisors Holdings LP and Citadel GP LLC: 0 2. Citadel Securities LLC: 0 3. Each of Citadel Securities Group LP and Citadel Securities GP LLC: 0 4. Mr. Griffin: 0 1. Each of Citadel Advisors LLC, Citadel Advisors Holdings LP and Citadel GP LLC: 5,325,269 2. Citadel Securities LLC: 8,843 3. Each of Citadel Securities Group LP and Citadel Securities GP LLC: 8,843 4. Mr. Griffin: 5,334,112 1. Each of Citadel Advisors LLC, Citadel Advisors Holdings LP and Citadel GP LLC: 0 2. Citadel Securities LLC: 0 3. Each of Citadel Securities Group LP and Citadel Securities GP LLC: 0 4. Mr. Griffin: 0 1. Each of Citadel Advisors LLC, Citadel Advisors Holdings LP and Citadel GP LLC: 5,325,269 2. Citadel Securities LLC: 8,843 3. Each of Citadel Securities Group LP and Citadel Securities GP LLC: 8,843 4. Mr. Griffin: 5,334,112 Y Y Y Y Y N By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under ?? 240.14a-11. Citadel Advisors LLC /s/ Seth Levy 08/14/2025 Citadel Advisors Holdings LP /s/ Seth Levy 08/14/2025 Citadel GP LLC /s/ Seth Levy 08/14/2025 Citadel Securities LLC /s/ Seth Levy 08/14/2025 Citadel Securities Group LP /s/ Seth Levy 08/14/2025 Citadel Securities GP LLC /s/ Seth Levy 08/14/2025 Kenneth Griffin /s/ Seth Levy 08/14/2025 * Seth Levy is signing on behalf of Kenneth Griffin as attorney-in-fact pursuant to a power of attorney previously filed with the Securities and Exchange Commission, and hereby incorporated by reference herein. The power of attorney was filed as an attachment to a filing by Citadel Advisors LLC on Schedule 13G for Allakos Inc. on October 13, 2023.