SCHEDULE 13G 0001831942 XXXXXXXX LIVE Common stock, par value $0.0001 per share 03/04/2026 0001835597 PepGen Inc. 713317105 321 Harrison Avenue 8th Floor Boston MA 02118 Rule 13d-1(c) Commodore Capital LP DE 0.00 3544101.00 0.00 3544101.00 3544101.00 5.1 IA PN Commodore Capital Master LP E9 0.00 3544101.00 0.00 3544101.00 3544101.00 5.1 PN Robert Egen Atkinson X1 0.00 3544101.00 0.00 3544101.00 3544101.00 5.1 HC IN Michael Kramarz X1 0.00 3544101.00 0.00 3544101.00 3544101.00 5.1 HC IN PepGen Inc. 321 Harrison Avenue, 8th Floor, Boston, MASSACHUSETTS, 02118. Commodore Capital LP Commodore Capital Master LP Robert Egen Atkinson Michael Kramarz Each a "Filer." The address for Commodore Capital LP, Robert Egen Atkinson, and Michael Kramarz is 444 Madison Avenue, Floor 35, New York, NY 10022. The address for Commodore Capital Master LP is c/o Maples Corporate Services Limited, Ugland House, South Church Street, PO Box 309, Grand Cayman KY1-1104, Cayman Islands. See Item 4 of the cover page for each Filer. Y See Item 9 of the cover page for each Filer. This report on Schedule 13G is being filed by Commodore Capital LP (the "Firm"), Commodore Capital Master LP ("Commodore Master"), Michael Kramarz, and Robert Egen Atkinson. The Firm is the investment manager to Commodore Master. As of March 4, 2026, the Firm may be deemed to beneficially own an aggregate of 3,544,101 shares of Common stock, par value $0.0001 per share (the "Common Stock"), of PepGen Inc. (the "Issuer"). The Firm, as the investment manager to Commodore Master, may be deemed to beneficially own these securities. Michael Kramarz and Robert Egen Atkinson are the managing partners of the Firm and exercise investment discretion with respect to these securities. Ownership percentages are based on 69,115,292 Common Stock reported as issued and outstanding as of February 26, 2026 in the Issuer's Annual Report on Form 10-K filed with the Securities and Exchange Commission on March 4, 2026. See Item 11 of the cover page for each Filer. See Item 5 of the cover page for each Filer. See Item 6 of the cover page for each Filer. See Item 7 of the cover page for each Filer. See Item 8 of the cover page for each Filer. Y N 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. Exhibit 1: Joint Filing Agreement Commodore Capital LP Michael Kramarz 03/11/2026 Commodore Capital Master LP Michael Kramarz 03/11/2026 Robert Egen Atkinson Robert Egen Atkinson 03/11/2026 Michael Kramarz Michael Kramarz 03/11/2026