Cartesian Therapeutics, Inc.

On May 15, 2025, Milos Miljkovic, our Chief Medical Officer, adopted a trading plan intended to satisfy the conditions under Rule 10b5-1(c) of the Exchange Act. Dr. Miljkovic’s plan provides for the exercise of vested stock options and the potential associated sale of up to 30,528 shares of our common stock and the potential sale of up to an additional 2,689 shares of our common stock until and including March 31, 2026. The foregoing exercises or sales, if any, will be made in accordance with the prices and formulas set forth in the plan and such plan terminates on the earlier of the date all the shares under the plan are sold and March 31, 2026.

Other than as set forth above, during the fiscal quarter ended June 30, 2025, no officer or director, as defined in Rule 16a-1(f) of the Exchange Act, informed us of theadoption, modification ortermination of any “Rule 10b5-1 trading arrangement” or a “non-Rule 10b5-1 trading arrangement,” as those terms are defined in Item 408 of Regulation S-K .