Allen signed a minor-league contract with the Diamondbacks on Tuesday and received an invitation to major-league spring training.
Allen spent all of last season in Triple-A, where he posted a 5.77 ERA and 1.74 WHIP across 103 innings between the Rockies' and Mariners' affiliates. He'll have a chance to make the Diamondbacks' bullpen during spring training, but Allen will most likely begin 2024 with Triple-A Reno.