Jax was optioned to Triple-A St. Paul on Wednesday, Dan Hayes of The Athletic reports.
Jax spent a week and a half in the major-league bullpen as a long reliever, and he posted an 8.64 ERA and 1.68 WHIP in 8.1 innings across three relief appearances. He'll now return to the minors after Caleb Thielbar (groin) was reinstated from the 10-day injured list.