RAPID MICRO BIOSYSTEMS, INC.

Why you received this proxy statement. You are viewing or have received these proxy materials because Rapid Micro Biosystems’ Board is soliciting your proxy to vote your shares at the Annual Meeting. This proxy statement includes information that we are required to provide to you under the rules of the SEC and that are designed to assist you in voting your shares.

Notice of Internet Availability of Proxy Materials. As permitted by SEC rules, Rapid Micro Biosystems is making this proxy statement and its 2025 Annual Report available to its Class A stockholders electronically online. On or about April 8, 2026, we mailed to our Class A stockholders a Notice of Internet Availability (the “Notice of Internet Availability”) containing instructions on how to access this proxy statement and our 2025 Annual Report and vote online. If you received a Notice of Internet Availability by mail, you will not receive a printed copy of the proxy materials in the mail unless you specifically request them. Instead, the Notice of Internet Availability instructs you on how to access and review all of the important information contained in this proxy statement and our 2025 Annual Report. The Notice of Internet Availability also instructs you on how you may submit your proxy online. If you received a Notice of Internet Availability by mail and would like to receive a printed copy of our proxy materials, you should follow the instructions for requesting such materials contained in the Notice of Internet Availability.

Printed Copies of Our Proxy Materials. If you received printed copies of our proxy materials, then instructions regarding how you can vote are contained on the proxy card included in the materials.

Householding. The SEC’s rules permit us to deliver a single set of proxy materials to one address shared by two or more of our stockholders. This delivery method is referred to as “householding” and can result in significant cost savings. To take advantage of this opportunity, we have delivered only one set of proxy materials to multiple stockholders who share an address, unless we received contrary instructions from the impacted stockholders prior to the mailing date. We agree to deliver promptly, upon written or oral request, a separate set of proxy materials, as requested, to any stockholder at the shared address to which a single set of those documents was delivered. If you prefer to receive separate copies of the proxy materials for the Annual Meeting or in the future, contact Broadridge Financial Solutions, Inc. at 1-866-540-7095 or in writing at Broadridge, Householding Department, 51 Mercedes Way, Edgewood, NY 11717.

If you are currently a stockholder sharing an address with another stockholder and wish to receive only one set of future proxy materials for your household, please contact Broadridge at the above phone number or address.