SCHEDULE 13G/A 0001103804 XXXXXXXX LIVE 5 Common Stock, $0.001 par value per share 09/30/2025 0001563880 Trevi Therapeutics, Inc. 89532M101 195 Church Street 16th Floor New Haven CT 06510 Rule 13d-1(c) VIKING GLOBAL INVESTORS LP b DE 0 5128875 0 5128875 5128875 N 4.2 PN See Item 4 Viking Global Opportunities Parent GP LLC b DE 0 5128875 0 5128875 5128875 N 4.2 OO See Item 4 Viking Global Opportunities GP LLC b DE 0 3436346 0 3436346 3436346 N 2.8 OO See Item 4 Viking Global Opportunities Portfolio GP LLC b DE 0 3436346 0 3436346 3436346 N 2.8 OO See Item 4 Viking Global Opportunities Illiquid Investments Sub-Master LP b E9 0 3436346 0 3436346 3436346 N 2.8 PN See Item 4 Viking Global Opportunities Drawdown GP LLC b DE 0 1692529 0 1692529 1692529 N 1.4 OO See Item 4 Viking Global Opportunities Drawdown Portfolio GP LLC b DE 0 1692529 0 1692529 1692529 N 1.4 OO See Item 4 Viking Global Opportunities Drawdown (Aggregator) LP b E9 0 1692529 0 1692529 1692529 N 1.4 PN See Item 4 HALVORSEN OLE ANDREAS b Q8 0 5128875 0 5128875 5128875 N 4.2 IN See Item 4 Ott David C. b X1 0 5128875 0 5128875 5128875 N 4.2 IN See Item 4 Shabet Rose Sharon b X1 0 5128875 0 5128875 5128875 N 4.2 IN See Item 4 Trevi Therapeutics, Inc. 195 Church Street, 16th Floor, New Haven, Connecticut, 06510 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"), Viking Global Opportunities Drawdown GP LLC ("VGOD GP"), Viking Global Opportunities Drawdown Portfolio GP LLC ("VGOD Portfolio GP"), Viking Global Opportunities Drawdown (Aggregator) LP ("VGOD"), 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, Opportunities Portfolio GP, VGOD GP and VGOD Portfolio GP are Delaware limited liability companies; VGOP and VGOD are Cayman Islands exempted limited partnerships; O. Andreas Halvorsen is a citizen of Norway; and David C. Ott and Rose S. Shabet are citizens of the United States. Y VGI: 5,128,875 VGI provides managerial services to VGOP and VGOD. VGI has the authority to dispose of and vote the shares of Common Stock that VGOP and VGOD directly own. VGI does not directly own any 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 that VGOP and VGOD directly own. VGI beneficially owns 5,128,875 shares of Common Stock consisting of 3,436,346 and 1,692,529 shares of Common Stock directly owned by VGOP and VGOD, respectively. Opportunities Parent: 5,128,875 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 that VGOP directly owns), and is the sole member of VGOD GP, which has the authority to dispose of and vote the shares of Common Stock controlled by VGOD Portfolio GP (which consists of the shares of Common Stock that VGOD directly owns). 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 that VGOP and VGOD directly own. Opportunities Parent beneficially owns 5,128,875 shares of Common Stock consisting of 3,436,346 and 1,692,529 shares of Common Stock directly owned by VGOP and VGOD, respectively. Opportunities GP: 3,436,346 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 that VGOP directly owns. In addition, Opportunities GP is the general partner of each of Viking Global Opportunities Intermediate LP, Viking Global Opportunities III LP, and Viking Global Opportunities LP. 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 that VGOP directly owns. Opportunities GP beneficially owns 3,436,346 shares of Common Stock consisting of 3,436,346 shares of Common Stock directly owned by VGOP. Opportunities Portfolio GP: 3,436,346 Opportunities Portfolio GP serves as the general partner of VGOP and has the authority to dispose of and vote the shares of Common Stock that VGOP directly owns. 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 that VGOP directly owns. Opportunities Portfolio GP beneficially owns 3,436,346 shares of Common Stock consisting of 3,436,346 shares of Common Stock directly owned by VGOP. VGOP: 3,436,346 VGOP has the authority to dispose of and vote the 3,436,346 shares of Common Stock that it owns, 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. VGOD GP: 1,692,529 VGOD GP serves as the sole member of VGOD Portfolio GP and has the authority to dispose of and vote the shares of Common Stock controlled by VGOD Portfolio GP, which consists of the shares of Common Stock that VGOD directly owns. In addition, VGOD GP is the general partner of each of Viking Global Opportunities Drawdown (Internal) LP, Viking Global Opportunities Drawdown (Onshore) LP, and Viking Global Opportunities Drawdown (Offshore) LP. VGOD GP does not directly own any shares of Common Stock. Based on Rule 13d-3 under the Act, VGOD GP may be deemed to beneficially own the shares of Common Stock that VGOD directly owns. VGOD GP beneficially owns 1,692,529 shares of Common Stock consisting of 1,692,529 shares of Common Stock directly owned by VGOD. VGOD Portfolio GP: 1,692,529 VGOD Portfolio GP serves as the general partner of VGOD and has the authority to dispose of and vote the shares of Common Stock that VGOD directly owns. VGOD Portfolio GP does not directly own any shares of Common Stock. Based on Rule 13d-3 under the Act, VGOD Portfolio GP may be deemed to beneficially own the shares of Common Stock that VGOD directly owns. VGOD Portfolio GP beneficially owns 1,692,529 shares of Common Stock consisting of 1,692,529 shares of Common Stock directly owned by VGOD. VGOD: 1,692,529 VGOD has the authority to dispose of and vote the 1,692,529 shares of Common Stock that it directly owns, which power may be exercised by VGOD Portfolio GP, and by VGI, an affiliate of VGOD Portfolio GP, which provides managerial services to VGOD. Viking Global Opportunities Drawdown (Offshore) LP (a Cayman Islands exempted limited partnership) and Viking Global Opportunities Drawdown (Internal) LP (a Delaware limited partnership), through its investment in Viking Global Opportunities Drawdown (Onshore) LP (a Delaware limited partnership), invest substantially all of their assets in VGOD. O. Andreas Halvorsen, David C. Ott and Rose S. Shabet: 5,128,875 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 that VGOP and VGOD directly own. Each of Mr. Halvorsen, Mr. Ott and Ms. Shabet beneficially owns 5,128,875 shares of Common Stock consisting of 3,436,346 and 1,692,529 shares of Common Stock directly owned by VGOP and VGOD, respectively. The percentages set forth herein are based on 121,776,855 shares of Common Stock outstanding as of July 31, 2025, as reported in the Issuer's quarterly report on Form 10-Q, filed with the Securities and Exchange Commission (the "Commission") on August 7, 2025. VGI: 4.2% Opportunities Parent: 4.2% Opportunities GP: 2.8% Opportunities Portfolio GP: 2.8% VGOP: 2.8% VGOD GP: 1.4% VGOD Portfolio GP: 1.4% VGOD: 1.4% O. Andreas Halvorsen, David C. Ott and Rose S. Shabet: 4.2% VGI: 0 Opportunities Parent: 0 Opportunities GP: 0 Opportunities Portfolio GP: 0 VGOP: 0 VGOD GP: 0 VGOD Portfolio GP: 0 VGOD: 0 O. Andreas Halvorsen, David C. Ott and Rose S. Shabet: 0 VGI: 5,128,875 Opportunities Parent: 5,128,875 Opportunities GP: 3,436,346 Opportunities Portfolio GP: 3,436,346 VGOP: 3,436,346 VGOD GP: 1,692,529 VGOD Portfolio GP: 1,692,529 VGOD: 1,692,529 O. Andreas Halvorsen, David C. Ott and Rose S. Shabet: 5,128,875 VGI: 0 Opportunities Parent: 0 Opportunities GP: 0 Opportunities Portfolio GP: 0 VGOP: 0 VGOD GP: 0 VGOD Portfolio GP: 0 VGOD: 0 O. Andreas Halvorsen, David C. Ott and Rose S. Shabet: 0 VGI: 5,128,875 Opportunities Parent: 5,128,875 Opportunities GP: 3,436,346 Opportunities Portfolio GP: 3,436,346 VGOP: 3,436,346 VGOD GP: 1,692,529 VGOD Portfolio GP: 1,692,529 VGOD: 1,692,529 O. Andreas Halvorsen, David C. Ott and Rose S. Shabet: 5,128,875 N 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 11/14/2025 Viking Global Opportunities Parent GP LLC /s/ Scott M. Hendler 11/14/2025 Viking Global Opportunities GP LLC /s/ Scott M. Hendler 11/14/2025 Viking Global Opportunities Portfolio GP LLC /s/ Scott M. Hendler 11/14/2025 Viking Global Opportunities Illiquid Investments Sub-Master LP /s/ Scott M. Hendler 11/14/2025 Viking Global Opportunities Drawdown GP LLC /s/ Scott M. Hendler 11/14/2025 Viking Global Opportunities Drawdown Portfolio GP LLC /s/ Scott M. Hendler 11/14/2025 Viking Global Opportunities Drawdown (Aggregator) LP /s/ Scott M. Hendler 11/14/2025 HALVORSEN OLE ANDREAS /s/ Scott M. Hendler 11/14/2025 Ott David C. /s/ Scott M. Hendler 11/14/2025 Shabet Rose Sharon /s/ Scott M. Hendler 11/14/2025 (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, VIKING GLOBAL OPPORTUNITIES ILLIQUID INVESTMENTS SUB-MASTER LP, VIKING GLOBAL OPPORTUNITIES DRAWDOWN GP LLC, VIKING GLOBAL OPPORTUNITIES DRAWDOWN PORTFOLIO GP LLC and VIKING GLOBAL OPPORTUNITIES DRAWDOWN (AGGREGATOR) 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, VIKING GLOBAL OPPORTUNITIES ILLIQUID INVESTMENTS SUB-MASTER LP, VIKING GLOBAL OPPORTUNITIES DRAWDOWN GP LLC, VIKING GLOBAL OPPORTUNITIES DRAWDOWN PORTFOLIO GP LLC and VIKING GLOBAL OPPORTUNITIES DRAWDOWN (AGGREGATOR) 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). (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, VIKING GLOBAL OPPORTUNITIES ILLIQUID INVESTMENTS SUB-MASTER LP, VIKING GLOBAL OPPORTUNITIES DRAWDOWN GP LLC, VIKING GLOBAL OPPORTUNITIES DRAWDOWN PORTFOLIO GP LLC and VIKING GLOBAL OPPORTUNITIES DRAWDOWN (AGGREGATOR) 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).