SCHEDULE 13G/A 0001952107 XXXXXXXX LIVE 2 Common Stock, $0.001 par value per share 06/30/2025 0001690585 DIANTHUS THERAPEUTICS, INC. 252828108 7 Times Square 43rd Floor New York NY 10036 Rule 13d-1(c) BCLS Fund III Investments, LP DE 0 2482250 0 2482250 2482250 N 7.5 PN DIANTHUS THERAPEUTICS, INC. 7 Times Square, 43rd Floor, New York, New York 10036 This Schedule 13G is being filed by BCLS Fund III Investments, LP, a Delaware limited partnership (the "Reporting Person"). Bain Capital Life Sciences Investors, LLC, a Delaware limited liability company ("BCLSI"), is the manager of Bain Capital Life Sciences III General Partner, LLC, a Delaware limited liability company ("BCLS Fund III GP"), which is the general partner of Bain Capital Life Sciences Fund III, L.P., a Delaware limited partnership ("BCLS Fund III"), which is the managing member of BCLS Fund III Investments GP, LLC, a Delaware limited liability company (together with the Reporting Person, BCLSI, BCLS Fund III GP and BCLS Fund III, the "Bain Capital Life Sciences Entities"), which is the general partner of the Reporting Person. As a result, BCLSI may be deemed to share voting and dispositive power with respect to the securities held by the Reporting Person. The principal business address for each of the Bain Capital Life Sciences Entities is 200 Clarendon Street, Boston, Massachusetts 02116. Each of the Bain Capital Life Sciences Entities is organized under the laws of the State of Delaware. Y As of the close of business on June 30, 2025, the Reporting Person held 1,481,917 shares of Common Stock and a pre-funded warrant to purchase up to 1,000,333 shares of Common Stock, together representing approximately 7.5% of the outstanding Common Stock. The Reporting Person is prohibited from exercising the pre-funded warrant if, as a result of such exercise, the Reporting Person 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 percentage of the outstanding shares of Common Stock held by the Reporting Person is based on (i) 32,176,482 shares of Common Stock outstanding as of June 30, 2025, as reported by the Issuer in its Quarterly Report on Form 10-Q for the quarter ended June 30, 2025, filed with the Securities and Exchange Commission on August 7, 2025 and (ii) 1,000,333 shares of Common Stock issuable upon the exercise of the pre-funded warrant held by the Reporting Person. 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. BCLS Fund III Investments, LP /s/ Ricky Sun 08/14/2025