Mariners Acquire Right-Hander Cooper Criswell, Designate Triple-A Workhorse Jhonathan Díaz

The Seattle Mariners added right-hander Cooper Criswell from the New York Mets for cash considerations and removed left-hander Jhonathan Díaz from the 40-man roster by designating him for assignment. The exchange is a clear example of roster tinkering that matters both for Seattle's big-league depth and for Triple-A Tacoma, where Díaz anchored the Rainiers' rotation in 2025.

Criswell, 29, brings big-league experience with Boston and previous time in the Mets organization. The low-cost acquisition reflects a league-wide emphasis on buying controllable pitching depth ahead of spring training and the season. For a club juggling innings and bullpen options, Criswell represents another arm that can be evaluated in camp for a role in the major league staff or as a depth option shuttled between Seattle and Tacoma.

Díaz had been a pillar for the Rainiers last season, going 11-6 in 27 starts and finishing the Pacific Coast League campaign with a 4.15 ERA. He led Tacoma in wins and was frequently called a workhorse as he logged the innings that kept the Triple-A rotation stable. Losing a southpaw who delivered that level of consistency in Triple-A translates into an immediate roster hole and a fan-facing loss for Tacoma, where minor league players often develop strong local followings.

The business mechanics of the move are straightforward: Criswell was acquired for cash considerations, a common economical route teams use to add experienced depth without surrendering prospects. Díaz's designation for assignment removes him from Seattle's 40-man roster and exposes him to waivers; he could be claimed by another club, traded, or outrighted back to the minors if he clears waivers. That process underscores the transactional reality for many Triple-A regulars who deliver solid results but remain vulnerable in roster crunches.

From a performance standpoint, the Mariners are balancing short-term needs and long-term depth. Criswell's past big-league exposure gives him a footprint on which to build in spring training, while Díaz's Triple-A success demonstrates his readiness to contribute either as a depth starter or a long reliever at the highest minor league level. For Tacoma, the Rainiers will need to replace Díaz's innings, creating opportunities for younger arms or reclamation projects to step into heavier workloads.

What happens next will be decided in the coming days as waiver wires move and spring training approaches. Fans in Seattle will watch Criswell's spring and hope he bolsters pitching depth, while Tacoma supporters will look to the Rainiers' rotation charts to see who fills the void left by Díaz's departure from the 40-man roster.