SCHEDULE 13G/A 0001773187 XXXXXXXX LIVE 3 Common Stock, par value $0.0001 per share 12/31/2025 0001840233 Xilio Therapeutics, Inc. 98422T100 828 Winter Street Suite 300 Waltham MA 02451 Rule 13d-1(c) Bain Capital Life Sciences Fund II, L.P. E9 0 992111 0 992111 992111 N 1.3 PN BCIP Life Sciences Associates, LP DE 0 120833 0 120833 120833 N 0.2 PN BCLS II Equity Opportunities, LP DE 0 6259742 0 6259742 6259742 N 8.5 PN BCLS II Investco, LP DE 0 0 0 0 0 N 0 PN Xilio Therapeutics, Inc. 828 Winter Street, Suite 300, Waltham, Massachusetts 02451 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"), BCLS II Equity Opportunities, LP, a Delaware limited partnership ("BCLS II Equity"), and BCLS II Investco, LP, a Delaware limited partnership ("BCLS II Investco" and, together with BCLS Fund II, BCIPLS and BCLS II Equity, 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. BCLS II Investco (GP), LLC, a Delaware limited liability company ("BCLS II Investco GP"), whose manager is BCLS Fund II, is the general partner of BCLS II Investco. 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 Fund II is the manager of BCLS II Equity Opportunities GP, LLC, a Delaware limited liability company ("BCLS II Equity GP" and, together with the Reporting Persons, BCLSI, BCLSI II, BCLS II Investco GP and Boylston, the "Bain Capital Life Sciences Entities"), which 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 February 17, 2026, 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 close of business on December 31, 2025, (i) BCLS Fund II held 992,111 shares of Common Stock, (ii) BCIPLS held 120,833 shares of Common Stock, (iii) BCLS II Equity held a pre-funded warrant to purchase 15,627,441 shares of Common Stock, and (iv) BCLS II Investco held no shares of Common Stock. BCLS II Equity is prohibited from exercising its pre-funded warrant if, as a result of such exercise, the Reporting Persons would collectively 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 "Beneficial Ownership Blocker"). Accordingly, pursuant to Rule 13d-3 of the Act and the relationships described herein, BCLS Fund II, BCIPLS and BCLS II Equity may be deemed to collectively beneficially own 9.99% of the outstanding shares of Common Stock, representing 7,372,686 shares of Common Stock as of December 31, 2025. The calculation of beneficial ownership of the Reporting Persons is based on (i) 67,540,930 shares of Common Stock outstanding, as reported by the Issuer in its Form 8-K filed with the Securities and Exchange Commission on January 5, 2026, and (ii) 6,259,742 shares of Common Stock issuable upon the exercise of the pre-funded warrant held by BCLS II Equity, which reflects the Beneficial Ownership Blocker. 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 02/17/2026 BCIP Life Sciences Associates, LP /s/ Andrew Hack 02/17/2026 BCLS II Equity Opportunities, LP /s/ Andrew Hack 02/17/2026 BCLS II Investco, LP /s/ Andrew Hack 02/17/2026