The Mariners optioned Mills to Triple-A Tacoma on Tuesday.
Mills was one of four players optioned or reassigned Tuesday in the Mariners' latest round of cuts at big-league camp. The 27-year-old righty closed last season at Tacoma, but he made 11 appearances at the big-league level in total in 2021, producing a 9.95 ERA and 2.05 WHIP across 12.2 innings.