Seattle Mariners Part Ways With 6-Year MLB Veteran

The Seattle Mariners have taken a significant step toward bolstering their pitching staff by selecting the contract of highly touted left-hander Kade Anderson from Double-A Arkansas.

To clear space on both the active and 40-man rosters for the move, the club designated left-hander Jhonathan Diaz for assignment. Diaz, a 29-year-old with six years of major league service time, now has five days for the organization to decide whether to outright him to the minors or release him outright.

This roster shuffle arrives as the Mariners cling to faint postseason hopes. They sit four games behind the Houston Astros in the American League West and three games back of the final Wild Card berth, with FanGraphs placing their playoff odds at roughly 33 percent. In that context, the arrival of a top prospect carries extra weight.

Anderson, the third overall selection in the 2025 draft, is set to make his major league debut Saturday night against the Chicago Cubs at T-Mobile Park. First pitch is scheduled for 7:15 p.m. Eastern. The 22-year-old earned the start after right-hander Bryan Woo was scratched from the assignment.

Anderson arrives with an impressive résumé: he was named Most Outstanding Player of the College World Series after helping LSU capture a national title, and many evaluators viewed him as the most big-league-ready arm in a strong college pitching class. He will become the first player from the 2025 draft class to reach the majors.

His numbers at Arkansas this season have been dominant. Across 18 starts and 93.1 innings, Anderson posted a 1.06 ERA while striking out 40.5 percent of the batters he faced.

That level of production made a promotion nearly inevitable, especially with the Mariners needing length in the rotation.

Diaz’s path to this point has been less linear. Originally a prospect in the Boston Red Sox system, he later spent time with the Los Angeles Angels before signing with Seattle as a minor-league free agent in 2024.

The Mariners recalled him from Triple-A Tacoma on August 19, and he appeared in the series finale against the Milwaukee Brewers the following day, working 1.1 innings. That outing represented his only big-league work in 2026.

Over the previous three seasons, he logged just 12.1 innings across seven appearances for Seattle. Having exhausted his minor-league options, the club elected to move on; this marks the third time since 2025 that Diaz has been designated for assignment by the organization, and he chose free agency on the prior two occasions.

Anderson’s early performance could influence longer-term decisions. With established starters Logan Gilbert and George Kirby both scheduled to reach free agency after the 2027 season, a strong showing from the young left-hander—and fellow prospect Ryan Sloan—may give the front office more flexibility to address other roster needs through trades or free-agent spending.

For now, though, the focus remains on Saturday’s matchup and whether Anderson can deliver the kind of outing that justifies the organization’s faith in his rapid rise.