X0609 4 2026-06-10 0001555279 908 Devices Inc. MASS 0001252546 HRUSOVSKY E KEVIN false C/O 908 DEVICES INC. 44 THIRD AVENUE BURLINGTON MA 01803 true false false false 0 Common Stock 2026-06-10 4 M 0 14083 A 165390 D Common Stock 329675 I See footnote Restricted Stock Units 2026-06-10 4 M 0 14083 0 D Common Stock 14083 0 D Restricted Stock Units 2026-06-11 4 A 0 13656 0 A Common Stock 13656 13656 D Stock Option (option to buy) 8.22 2026-06-11 4 A 0 6209 0 A 2036-06-10 Common Stock 6209 6209 D Each Restricted Stock Unit ("RSU") represents a contingent right to receive one share of Common Stock, par value $0.001, when vested. The securities are owned directly by the E. Kevin Hrusovsky 2012 Irrevocable Trust. The reporting person's spouse and children are trustees of E. Kevin Hrusovsky 2012 Irrevocable Trust and have joint voting and dispositive control with respect to all securities held by E. Kevin Hrusovsky 2012 Irrevocable Trust and the reporting person may be deemed to be the beneficial owner of the securities held by E. Kevin Hrusovsky 2012 Irrevocable Trust. The RSUs became fully vested on June 10, 2026, the day prior to the 2026 Annual Meeting of the Stockholders of 908 Devices Inc. The RSUs have no expiration date. The RSUs become fully vested on June 11, 2027 or the day prior to the 2027 Annual Meeting of the Stockholders of 908 Devices Inc., whichever occurs first, subject to the reporting person's continued service through the applicable vesting date, provided that, if the reporting person terminates their service for any reason, then a prorated number of RSUs will vest. The RSUs have no expiration date. The shares underlying the option become vested and exercisable in substantially equal monthly installments over the 12 months following June 11, 2026, subject to the reporting person's continued service through the applicable vesting date. /s/ Mark S. Levine, Attorney-in-Fact 2026-06-12