The Mariners optioned Simpson to Triple-A Tacoma on Friday.
Simpson was acquired by the Mariners from the Marlins in mid-February. The 28-year-old southpaw made his major-league debut for Miami in 2025 and appeared in 31 games, posting a 7.34 ERA, 1.83 WHIP and 36:22 K:BB across 30.2 innings. Simpson will open the 2026 season in Triple-A but could get called up to the majors if the Mariners need a left-hander out of the bullpen.