X0202 SCHEDULE 13G/A 0001687968 XXXXXXXX LIVE 1 Class A Common Stock, par value $0.01 per share 06/30/2026 0001380106 Rapid Micro Biosystems, Inc. 75340L104 25 Hartwell Avenue Lexington MA 02421 Rule 13d-1(d) Bain Capital Life Sciences Fund, L.P. E9 0 7651369 0 7651369 7651369 N 16.76 PN BCIP Life Sciences Associates, LP DE 0 783191 0 783191 783191 N 1.72 PN Rapid Micro Biosystems, Inc. 25 Hartwell Avenue, Lexington, Massachusetts 02421 This Schedule 13G is being filed jointly by Bain Capital Life Sciences Fund, L.P., a Cayman Islands exempted limited partnership ("BCLS Fund I"), and BCIP Life Sciences Associates, LP, a Delaware limited partnership ("BCIPLS" and, together with BCLS Fund I, the "Reporting Persons"). Bain Capital Life Sciences Investors, LLC, a Delaware limited liability company ("BCLSI"), is the general partner of Bain Capital Life Sciences Partners, LP, a Cayman Islands exempted limited partnership ("BCLSP"), which is the general partner of BCLS Fund I. Boylston Coinvestors, LLC, a Delaware limited liability company ("Boylston" and, together with the Reporting Persons, BCLSI and BCLSP, the "Bain Capital Life Sciences Entities"), is the general partner of BCIPLS. BCLSI governs the investment strategy and decision-making process with respect to investments held by BCIPLS. 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 August 14, 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 June 30, 2026, (i) BCLS Fund I held 7,651,369 shares of Class A Common Stock, representing approximately 16.8% of the outstanding shares of Class A Common Stock, (ii) BCIPLS held 783,191 shares of Class A Common Stock, representing approximately 1.7% of the outstanding shares of Class A Common Stock, and (iii) BCLS Investco, LP, whose ultimate general partner is BCLSI, held a Pre-Funded Warrant to purchase up to 1,463,000 shares of Class A Common Stock, a Series A Warrant to purchase up to 1,463,000 shares of Class A Common Stock (or pre-funded warrants in lieu thereof), and a Series B Warrant to purchase up to 1,463,000 shares of Class A Common Stock (or pre-funded warrants in lieu thereof). BCLS Investco, LP is prohibited from exercising the Pre-Funded Warrant, Series A Warrant, or Series B Warrant if, as a result of such exercise, BCLS Investco, LP, together with its affiliates (including the Reporting Persons), would collectively beneficially own more than 9.99% of the total number of shares of Class A Common Stock then issued and outstanding immediately after giving effect to the exercise. Accordingly, pursuant to Rule 13d-3 of the Act and the relationships described herein, BCLS Investco, LP is not deeemed to beneficially own any shares of Class A Common Stock. The calculation of beneficial ownership is based on 45,660,027 shares of Class A Common Stock outstanding as of July 31, 2026, as reported by the Issuer in its Quarterly Report on Form 10-Q for the quarter ended June 30, 2026, filed with the Securities and Exchange Commission on August 7, 2026. See Item 4(a) hereof. 0 See Item 4(a) hereof. 0 See Item 4(a) hereof. Y Y Y Y Y Y Bain Capital Life Sciences Fund, L.P. /s/ Andrew Hack 08/14/2026 BCIP Life Sciences Associates, LP /s/ Andrew Hack 08/14/2026