X0306 4 2020-10-27 0 0001822462 Foghorn Therapeutics Inc. FHTX 0001724575 Flagship Ventures Fund V General Partner LLC 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE MA 02142 0 0 1 0 0001725004 Flagship Ventures Opportunities Fund I General Partner LLC 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE MA 02142 0 0 1 0 0001826217 Flagship Pioneering Special Opportunities Fund II General Partner LLC 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE MA 02142 0 0 1 0 0001627639 Flagship Ventures Fund V, L.P. 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE MA 02142 0 0 1 0 0001677345 Flagship Ventures Opportunities Fund I, L.P. 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE MA 02142 0 0 1 0 0001761283 Flagship Pioneering Special Opportunities Fund II, L.P. 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE MA 02142 0 0 1 0 0001400240 Flagship Pioneering Inc. 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE MA 02142 0 0 1 0 0001222012 AFEYAN NOUBAR 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE MA 0 0 1 0 Common Stock 2020-10-27 4 C 0 4054054 A 4054054 I See Footnote Common Stock 2020-10-27 4 C 0 4504504 A 8558558 I See Footnote Common Stock 2020-10-27 4 C 0 722320 A 9280878 I See Footnote Common Stock 2020-10-27 4 P 0 50000 16.00 A 9330878 I See Footnote Common Stock 2020-10-27 4 C 0 1441441 A 1441441 I See Footnote Common Stock 2020-10-27 4 P 0 50000 16.00 A 1491441 I See Footnote Common Stock 2020-10-27 4 C 0 1801801 A 1801801 I See Footnote Common Stock 2020-10-27 4 P 0 50000 16.00 A 1851801 I See Footnote Series A-1 Convertible Preferred Stock 2020-10-27 4 C 0 7500000 D Common Stock 4054054 0 I See Footnote Series A-2 Convertible Preferred Stock 2020-10-27 4 C 0 8333333 D Common Stock 4504504 0 I See Footnote Series B Convertible Preferred Stock 2020-10-27 4 C 0 1336293 D Common Stock 722320 0 I See Footnote Series B Convertible Preferred Stock 2020-10-27 4 C 0 2666666 D Common Stock 1441441 0 I See Footnote Series B Convertible Preferred Stock 2020-10-27 4 C 0 3333333 D Common Stock 1801801 0 I See Footnote The Series A-1 Convertible Preferred Stock, Series A-2 Convertible Preferred Stock, and Series B Convertible Preferred Stock (collectively, the "Preferred Stock") is convertible into the number of shares of the Registrant's common stock shown in Table II, column 7 and has no expiration date. The Preferred Stock automatically converted into common stock upon the closing of the Registrant's initial public offering, which occurred on October 27, 2020. Shares held by Flagship Ventures Fund V, L.P. ("Flagship Fund V"). Flagship Ventures Fund V General Partner LLC ("Fund V GP") is the general partner of Flagship Fund V. Noubar B. Afeyan Ph.D. serves as the sole manager of Fund V GP. Each of Fund V GP and Noubar B. Afeyan Ph.D. disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein. Shares held by Flagship Ventures Opportunities Fund I, L.P. ("Flagship Opportunities Fund I"). Flagship Ventures Opportunities Fund I General Partner LLC ("Opportunities Fund I GP") is the general partner of Flagship Opportunities Fund I. Noubar B. Afeyan Ph.D. serves as the sole manager of Opportunities Fund I GP. Each of Opportunities Fund I GP and Noubar B. Afeyan Ph.D. disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein. Shares held by Flagship Pioneering Special Opportunities Fund II, L.P. ("Flagship Opportunities Fund II"). Flagship Pioneering Special Opportunities Fund II General Partner LLC ("Opportunities Fund II GP") is the general partner of Flagship Opportunities Fund II. Flagship Pioneering, Inc. ("Flagship Pioneering") is the manager of Opportunities Fund II GP. Noubar B. Afeyan, Ph.D. is sole director of Flagship Pioneering. Each of Noubar B. Afeyan Ph.D., Flagship Pioneering, and Opportunities Fund II GP disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein. Flagship Ventures Fund V General Partner LLC, By:, Name: Noubar B. Afeyan Ph.D., Title: Manager 2020-10-29 Flagship Ventures Opportunities Fund I General Partner LLC, By:, Name: Noubar B. Afeyan Ph.D., Title: Manager 2020-10-29 Flagship Pioneering Special Opportunities Fund II General Partner LLC, By: Flagship Pioneering, Inc., Name: Noubar B. Afeyan Ph.D., Title: CEO 2020-10-29 Flagship Ventures Fund V, L.P., By: Flagship Ventures Fund V General Partner LLC, its general partner, By: /s/ Noubar B. Afeyan Ph.D., Title: Manager 2020-10-29 Flagship Ventures Opportunities Fund I, L.P., By: Flagship Ventures Opportunities Fund I General Partner LLC, its general partner, By: /s/ Noubar B. Afeyan Ph.D., Title: Manager 2020-10-29 Flagship Pioneering Special Opportunities Fund II, L.P., By: Flagship Pioneering Special Opportunities Fund II General Partner LLC, By: Flagship Pioneering, Inc. its manager, By: /s/ Noubar B. Afeyan Ph.D., Title: CEO, Flagship Pioneering, Inc. 2020-10-29 Flagship Pioneering, Inc., By:, Name: Noubar B. Afeyan Ph.D., Title: CEO 2020-10-29 /s/ Noubar B. Afeyan Ph.D. 2020-10-29