SCHEDULE 13G 0001103804 XXXXXXXX LIVE Common Stock, par value $0.0001 per share 09/26/2025 0001835597 PepGen Inc. 713317105 321 Harrison Avenue 8th Floor Boston MA 02118 Rule 13d-1(c) VIKING GLOBAL INVESTORS LP b DE 0 3482434 0 3482434 3482434 N 5.1 PN See Item 4 Viking Global Opportunities Parent GP LLC b DE 0 3482434 0 3482434 3482434 N 5.1 OO See Item 4 Viking Global Opportunities GP LLC b DE 0 3482434 0 3482434 3482434 N 5.1 OO See Item 4 Viking Global Opportunities Portfolio GP LLC b DE 0 3482434 0 3482434 3482434 N 5.1 OO See Item 4 Viking Global Opportunities Illiquid Investments Sub-Master LP b E9 0 3482434 0 3482434 3482434 N 5.1 PN See Item 4 HALVORSEN OLE ANDREAS b Q8 0 3482434 0 3482434 3482434 N 5.1 IN See Item 4 Ott David C. b X1 0 3482434 0 3482434 3482434 N 5.1 IN See Item 4 Shabet Rose Sharon b X1 0 3482434 0 3482434 3482434 N 5.1 IN See Item 4 PepGen Inc. 321 Harrison Avenue, 8th Floor, Boston, Massachusetts, 02118 Viking Global Investors LP ("VGI"), Viking Global Opportunities Parent GP LLC ("Opportunities Parent"), Viking Global Opportunities GP LLC ("Opportunities GP"), Viking Global Opportunities Portfolio GP LLC ("Opportunities Portfolio GP"), Viking Global Opportunities Illiquid Investments Sub-Master LP ("VGOP"), O. Andreas Halvorsen, David C. Ott and Rose S. Shabet (collectively, the "Reporting Persons") The business address of each of the Reporting Persons is: 600 Washington Boulevard, Floor 11, Stamford, Connecticut 06901. VGI is a Delaware limited partnership; Opportunities Parent, Opportunities GP and Opportunities Portfolio GP are Delaware limited liability companies; VGOP is a Cayman Islands exempted limited partnership; O. Andreas Halvorsen is a citizen of Norway; and David C. Ott and Rose S. Shabet are citizens of the United States. Y VGI: 3,482,434 VGI provides managerial services to VGOP. VGI has the authority to dispose of and vote the shares of Common Stock. Based on Rule 13d-3 under the Securities Exchange Act of 1934, as amended (the "Act"), VGI may be deemed to beneficially own the shares of Common Stock directly held by VGOP. VGI does not directly own any shares of Common Stock. VGI beneficially owns 3,482,434 shares of Common Stock consisting of 3,482,434 shares of Common Stock directly and beneficially owned by VGOP. Opportunities Parent: 3,482,434 Opportunities Parent is the sole member of Opportunities GP, which has the authority to dispose of and vote the shares of Common Stock controlled by Opportunities Portfolio GP, which consists of the shares of Common Stock directly held by VGOP. Opportunities Parent does not directly own any shares of Common Stock. Based on Rule 13d-3 under the Act, Opportunities Parent may be deemed to beneficially own the shares of Common Stock directly held by VGOP. Opportunities Parent beneficially owns 3,482,434 shares of Common Stock consisting of 3,482,434 shares of Common Stock directly owned by VGOP. Opportunities GP: 3,482,434 Opportunities GP serves as the sole member of Opportunities Portfolio GP and has the authority to dispose of and vote the shares of Common Stock controlled by Opportunities Portfolio GP, which consists of the shares of Common Stock directly held by VGOP. Opportunities GP does not directly own any shares of Common Stock. Based on Rule 13d-3 under the Act, Opportunities GP may be deemed to beneficially own the shares of Common Stock directly held by VGOP. Opportunities GP beneficially owns 3,482,434 shares of Common Stock consisting of 3,482,434 shares of Common Stock directly owned by VGOP. Opportunities Portfolio GP: 3,482,434 Opportunities Portfolio GP serves as the general partner of VGOP and has the authority to dispose of and vote the shares of Common Stock directly owned by VGOP. Opportunities Portfolio GP does not directly own any shares of Common Stock. Based on Rule 13d-3 under the Act, Opportunities Portfolio GP may be deemed to beneficially own the shares of Common Stock directly held by VGOP. Opportunities Portfolio GP beneficially owns 3,482,434 shares of Common Stock consisting of 3,482,434 shares of Common Stock directly owned by VGOP. VGOP: 3,482,434 VGOP has the authority to dispose of and vote the 3,482,434 shares of Common Stock directly owned by it, which power may be exercised by its general partner, Opportunities Portfolio GP, and by VGI, an affiliate of Opportunities Portfolio GP, which provides managerial services to VGOP. Viking Global Opportunities LP (a Delaware limited partnership) and Viking Global Opportunities III LP (a Cayman Islands exempted limited partnership), through its investment in Viking Global Opportunities Intermediate LP (a Cayman Islands exempted limited partnership), invest substantially all of their assets in Viking Global Opportunities Master LP (a Cayman Islands exempted limited partnership), which in turn invests through VGOP. O. Andreas Halvorsen, David C. Ott and Rose S. Shabet: 3,482,434 Mr. Halvorsen, Mr. Ott and Ms. Shabet, as Executive Committee Members of Viking Global Partners LLC (general partner of VGI) and Opportunities Parent, have shared authority to dispose of and vote the shares of Common Stock beneficially owned by VGI and Opportunities Parent. None of Mr. Halvorsen, Mr. Ott and Ms. Shabet directly owns any shares of Common Stock. Based on Rule 13d-3 under the Act, each may be deemed to beneficially own the shares of Common Stock directly held by VGOP. Mr. Halvorsen, Mr. Ott and Ms. Shabet each beneficially own 3,482,434 shares of Common Stock consisting of 3,482,434 shares of Common Stock directly owned by VGOP. The percentages set forth herein are based on 68,737,224 shares of Common Stock outstanding following the Issuer's underwritten offering that closed on September 26, 2025, and after the underwriters exercised their option to purchase additional shares of Common Stock in full, as reported in the Issuer's prospectus on Form 424B5, filed with the Securities and Exchange Commission (the "Commission") on September 25, 2025, and the Issuer's current report on Form 8-K, filed with the Commission on September 26, 2025. VGI: 5.1% Opportunities Parent: 5.1% Opportunities GP: 5.1% Opportunities Portfolio GP: 5.1% VGOP: 5.1% O. Andreas Halvorsen, David C. Ott and Rose S. Shabet: 5.1% VGI: 0 Opportunities Parent: 0 Opportunities GP: 0 Opportunities Portfolio GP: 0 VGOP: 0 O. Andreas Halvorsen, David C. Ott and Rose S. Shabet: 0 VGI: 3,482,434 Opportunities Parent: 3,482,434 Opportunities GP: 3,482,434 Opportunities Portfolio GP: 3,482,434 VGOP: 3,482,434 O. Andreas Halvorsen, David C. Ott and Rose S. Shabet: 3,482,434 VGI: 0 Opportunities Parent: 0 Opportunities GP: 0 Opportunities Portfolio GP: 0 VGOP: 0 O. Andreas Halvorsen, David C. Ott and Rose S. Shabet: 0 VGI: 3,482,434 Opportunities Parent: 3,482,434 Opportunities GP: 3,482,434 Opportunities Portfolio GP: 3,482,434 VGOP: 3,482,434 O. Andreas Halvorsen, David C. Ott and Rose S. Shabet: 3,482,434 Y N The response to Item 4 is incorporated by reference herein. 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 A - JOINT FILING AGREEMENT VIKING GLOBAL INVESTORS LP /s/ Scott M. Hendler 10/03/2025 Viking Global Opportunities Parent GP LLC /s/ Scott M. Hendler 10/03/2025 Viking Global Opportunities GP LLC /s/ Scott M. Hendler 10/03/2025 Viking Global Opportunities Portfolio GP LLC /s/ Scott M. Hendler 10/03/2025 Viking Global Opportunities Illiquid Investments Sub-Master LP /s/ Scott M. Hendler 10/03/2025 HALVORSEN OLE ANDREAS /s/ Scott M. Hendler 10/03/2025 Ott David C. /s/ Scott M. Hendler 10/03/2025 Shabet Rose Sharon /s/ Scott M. Hendler 10/03/2025 (1) Scott M. Hendler is signing on behalf of O. Andreas Halvorsen, individually and as an Executive Committee Member of VIKING GLOBAL PARTNERS LLC, on behalf of VIKING GLOBAL INVESTORS LP, and as an Executive Committee Member of VIKING GLOBAL OPPORTUNITIES PARENT GP LLC, on behalf of itself and VIKING GLOBAL OPPORTUNITIES GP LLC, VIKING GLOBAL OPPORTUNITIES PORTFOLIO GP LLC, and VIKING GLOBAL OPPORTUNITIES ILLIQUID INVESTMENTS SUB-MASTER LP, pursuant to an authorization and designation letter dated February 9, 2021, which was previously filed with the Commission as an exhibit to a Form 13G filed by Mr. Halvorsen on February 12, 2021 (SEC File No. 005-49737). (2) Scott M. Hendler is signing on behalf of David C. Ott, individually and as an Executive Committee Member of VIKING GLOBAL PARTNERS LLC, on behalf of VIKING GLOBAL INVESTORS LP, and as an Executive Committee Member of VIKING GLOBAL OPPORTUNITIES PARENT GP LLC, on behalf of itself and VIKING GLOBAL OPPORTUNITIES GP LLC, VIKING GLOBAL OPPORTUNITIES PORTFOLIO GP LLC, and VIKING GLOBAL OPPORTUNITIES ILLIQUID INVESTMENTS SUB-MASTER LP, pursuant to an authorization and designation letter dated February 9, 2021, which was previously filed with the Commission as an exhibit to a Form 13G filed by Mr. Ott on February 12, 2021 (SEC File No. 005-49737). (3) Scott M. Hendler is signing on behalf of Rose S. Shabet, individually and as an Executive Committee Member of VIKING GLOBAL PARTNERS LLC, on behalf of VIKING GLOBAL INVESTORS LP, and as an Executive Committee Member of VIKING GLOBAL OPPORTUNITIES PARENT GP LLC, on behalf of itself and VIKING GLOBAL OPPORTUNITIES GP LLC, VIKING GLOBAL OPPORTUNITIES PORTFOLIO GP LLC, and VIKING GLOBAL OPPORTUNITIES ILLIQUID INVESTMENTS SUB-MASTER LP, pursuant to an authorization and designation letter dated February 9, 2021, which was previously filed with the Commission as an exhibit to a Form 13G filed by Ms. Shabet on February 12, 2021 (SEC File No. 005-49737).