X0508 4 2023-11-07 1 0001907108 Lexeo Therapeutics, Inc. LXEO 0001757917 Omega Fund VI, L.P. 888 BOYLSTON STREET, SUITE 1111 BOSTON MA 02199 0 0 1 0 0001826592 Omega Fund VI GP, L.P. 888 BOYLSTON STREET, SUITE 1111 BOSTON MA 02199 0 0 1 0 0001826584 Omega Fund VI GP Manager, Ltd. 888 BOYLSTON STREET, SUITE 1111 BOSTON MA 02199 0 0 1 0 0001361712 Stampacchia Otello C/O OMEGA FUNDS 888 BOYLSTON ST., SUITE 1111 BOSTON MA 02199 0 0 1 0 0001722050 Nessi Claudio C/O OMEGA FUNDS 888 BOYLSTON STREET, SUITE 1111 BOSTON MA 0 0 1 0 0001652863 Paster Anne-Mari C/O OMEGA FUNDS 888 BOYLSTON STREET, SUITE 1111 BOSTON MA 02119 0 0 1 0 0 Common Stock 2023-11-07 4 C 0 1415865 A 1415865 D Common Stock 2023-11-07 4 C 0 287213 A 1703078 D Common Stock 2023-11-07 4 P 0 454545 11.00 A 2157623 D Series A convertible preferred stock 2023-11-07 4 C 0 14999999 D Common Stock 1415865 0 D Series B convertible preferred stock 2023-11-07 4 C 0 2615533 D Common Stock 287213 0 D Upon the closing of the Issuer's initial public offering, each share of Series A convertible preferred stock automatically converted into shares of the Issuer's common stock on a one-for-10.594230 basis. The shares had no expiration date. Upon the closing of the Issuer's initial public offering, each share of Series B convertible preferred stock automatically converted into shares of the Issuer's common stock on a one-for-9.106601 basis, which reflects an anti-dilution adjustment to the conversion ratio pursuant to a provision of the Series B convertible preferred stock based on the pricing of the initial public offering (as described in the Reporting Person's Form 3). The shares had no expiration date. /s/ Otello Stampacchia, authorized signatory 2023-11-09 /s/ Otello Stampacchia, authorized signatory 2023-11-09 /s/ Otello Stampacchia, authorized signatory 2023-11-09 /s/ Otello Stampacchia, authorized signatory 2023-11-09 /s/ Otello Stampacchia, authorized signatory 2023-11-09 /s/ Otello Stampacchia, authorized signatory 2023-11-09