SCHEDULE 13G 0001773187 XXXXXXXX LIVE Common Stock, par value $0.0001 per share 10/17/2025 0001662579 C4 Therapeutics, Inc. 12529R107 490 Arsenal Way Suite 120 Watertown MA 02472 Rule 13d-1(c) Bain Capital Life Sciences Fund II, L.P. E9 0 991188 0 991188 991188 N 1.07 PN BCIP Life Sciences Associates, LP DE 0 120722 0 120722 120722 N 0.13 PN BCLS II Equity Opportunities, LP DE 0 6060000 0 6060000 6060000 N 6.25 PN C4 Therapeutics, Inc. 490 Arsenal Way, Suite 120, Watertown, Massachusetts 02472 This Schedule 13G is being filed jointly by Bain Capital Life Sciences Fund II, L.P., a Cayman Islands exempted limited partnership ("BCLS Fund II"), BCIP Life Sciences Associates, LP, a Delaware limited partnership ("BCIPLS"), and BCLS II Equity Opportunities, LP, a Delaware limited partnership ("BCLS II Equity" and, together with BCLS Fund II and BCIPLS, the "Reporting Persons"). Bain Capital Life Sciences Investors, LLC, a Delaware limited liability company ("BCLSI"), is the manager of Bain Capital Life Sciences Investors II, LLC, a Cayman Islands limited liability company ("BCLSI II"), which is the general partner of BCLS Fund II. Boylston Coinvestors, LLC, a Delaware limited liability company ("Boylston"), is the general partner of BCIPLS. BCLSI governs the investment strategy and decision-making process with respect to investments held by BCIPLS. BCLS II Equity Opportunities GP, LLC, a Delaware limited liability company ("BCLS II Equity GP" and, together with the Reporting Persons, BCLSI, BCLSI II and Boylston, the "Bain Capital Life Sciences Entities"), whose manager is BCLS Fund II, is the general partner of BCLS II Equity. As a result, BCLSI may be deemed to share voting and dispositive power with respect to the securities held by the Reporting Persons. The Reporting Persons have entered into a Joint Filing Agreement, dated October 24, 2025, pursuant to which the Reporting Persons have agreed to file this Schedule 13G jointly in accordance with the provisions of Rule 13d-1(k)(1) promulgated under the Act. The principal business address for each of the Bain Capital Life Sciences Entities is 200 Clarendon Street, Boston, Massachusetts 02116. See Item 2(a) hereof. Y As of the date hereof, (i) BCLS Fund II holds 991,188 shares of Common Stock; (ii) BCIPLS holds 120,722 shares of Common Stock; and (iii) BCLS II Equity holds 2,020,000 shares of Common Stock and warrants to purchase an aggregate of 4,040,000 Common Stock. As a result of the foregoing and the relationships described in Item 2(a), the Reporting Persons may be deemed to collectively beneficially own an aggregate of 7,171,910 shares of Common Stock, representing approximately 7.4% of the outstanding Common Stock. BCLS II Equity is prohibited from exercising the warrants to purchase Common Stock if, as a result of such exercise, the Reporting Persons would beneficially own more than 9.99% of the total number of shares of Common Stock then issued and outstanding immediately after giving effect to the exercise. The calculation of the beneficial ownership of the Reporting Persons is based on (i) 92,902,083 shares of Common Stock outstanding, as reported by the Issuer in its prospectus supplement filed with the Securities and Exchange Commission on October 16, 2025 and (ii) 4,040,000 shares of Common Stock issuable upon the exercise of warrants held by BCLS II Equity. See Item 4(a) hereof. 0 See Item 4(a) hereof. 0 See Item 4(a) hereof. Y 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. Bain Capital Life Sciences Fund II, L.P. /s/ Andrew Hack 10/24/2025 BCIP Life Sciences Associates, LP /s/ Andrew Hack 10/24/2025 BCLS II Equity Opportunities, LP /s/ Andrew Hack 10/24/2025