Additional Proxy Soliciting Materials - Form DEFA14A

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 03Z1DB + + Important Notice Regarding the Availability of Proxy Materials for 908 Devices Inc. Stockholder Meeting to be Held on June 13, 2024. 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 2024 Proxy Statement and 2023 Annual Report on Form 10-K to shareholders 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 29, 2024 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 [email protected] with "Proxy Materials 908 Devices" 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 29, 2024. 908 Devices Inc. 2024 Annual Meeting of Stockholders will be held on June 13, 2024, at 10:00 a.m. Eastern Time, virtually via the internet at meetnow.global/MMMY6GC. 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 and FOR Proposal 2: 1. To elect two Class I directors to hold office until the 2027 annual meeting of stockholders. 01 - Fenel M. Eloi 02 - Jeffery P. George 2. To ratify, on an advisory basis, the appointment of PricewaterhouseCoopers LLP as our independent registered public accounting firm for the fiscal year ending December 31, 2024. 3. 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