The Tigers informed Vest on Tuesday that he'll be included in the team's Opening Day bullpen, Evan Woodbery of MLive.com reports.
Fellow non-roster relievers Drew Hutchison and Jacob Barnes are also set to make the team, so Detroit will need to make corresponding transactions to clear spots on the 40-man roster for all three pitchers. Vest made his big-league debut with Seattle in 2021, appearing in 32 games out of the Mariners' bullpen and submitting a 6.17 ERA and 1.60 WHIP in 35 innings. He'll likely be relegated to low-leverage work to begin his time with the Tigers.