SEC Form DEFA14A filed by 908 Devices Inc.

Step 1: Go to www.envisionreports.com/MASS. Step 2: Click on Cast Your Vote or Request Materials. Step 3: Follow the instructions on the screen to log in. www.envisionreports.com/MASS Online Go to www.envisionreports.com/MASS or scan the QR code — login details are located in the shaded bar below. Stockholder Meeting Notice 049KMB Important Notice Regarding the Availability of Proxy Materials for 908 Devices Inc. Stockholder Meeting to be Held on June 11, 2026. Under Securities and Exchange Commission rules, you are receiving this notice that the proxy materials for the annual stockholders’ meeting are available on the Internet. Follow the instructions below to view the materials and vote online or request a copy. The items to be voted on and location of the annual meeting are on the reverse side. Your vote is important! This communication presents only an overview of the more complete proxy materials that are available to you on the Internet. We encourage you to access and review all of the important information contained in the proxy materials before voting. The Proxy Statement and 2025 Annual Report on Form 10-K to stockholders are available at: Obtaining a Copy of the Proxy Materials – If you want to receive a copy of the proxy materials, you must request one. There is no charge to you for requesting a copy. Please make your request as instructed on the reverse side on or before May 27, 2026 to facilitate timely delivery. 2NOT Easy Online Access — View your proxy materials and vote. When you go online, you can also help the environment by consenting to receive electronic delivery of future materials. Step 4: Make your selections as instructed on each screen for your delivery preferences. Step 5: Vote your shares.

Here’s how to order a copy of the proxy materials and select delivery preferences: Current and future delivery requests can be submitted using the options below. If you request an email copy, you will receive an email with a link to the current meeting materials. PLEASE NOTE: You must use the number in the shaded bar on the reverse side when requesting a copy of the proxy materials. — Internet – Go to www.envisionreports.com/MASS. Click Cast Your Vote or Request Materials. — Phone – Call us free of charge at 1-866-641-4276. — Email – Send an email to investorvote@computershare.com with “Proxy Materials 908 Devices Inc.” in the subject line. Include your full name and address, plus the number located in the shaded bar on the reverse side, and state that you want a paper copy of the meeting materials. To facilitate timely delivery, all requests for a paper copy of proxy materials must be received by May 27, 2026. 908 Devices Inc. 2026 Annual Meeting of Stockholders will be held on June 11, 2026, at 10:00 a.m. ET, virtually via the internet at meetnow.global/MC2YHGH. To access the virtual meeting, you must have the information that is printed in the shaded bar located on the reverse side of this form. Proposals to be voted on at the meeting are listed below along with the Board of Directors’ recommendations. The Board of Directors recommend a vote FOR all the nominees listed, FOR Proposals 2 and 3, and 1 YEAR for Proposal 4: 1. To elect three Class III directors to hold office until the 2029 annual meeting of stockholders. 01 - Keith L. Crandell 02 - Christopher Brown, Ph.D. 03 - E. Kevin Hrusovsky 2. To ratify the appointment of PricewaterhouseCoopers LLP as our independent registered public accounting firm for the fiscal year ending December 31, 2026. 3. To approve, on a non-binding advisory basis, the compensation of the Company’s named executive officers. 4. To hold an advisory vote on the frequency of holding future non-binding advisory votes on the compensation of our named executive officers. 5. To transact any other business that properly comes before the Annual Meeting and at any adjournments and postponements thereof. PLEASE NOTE – YOU CANNOT VOTE BY RETURNING THIS NOTICE. To vote your shares you must go online or request a paper copy of the proxy materials to receive a proxy card. Stockholder Meeting Notice