Seattle Mariners starting pitcher Luis Castillo is on the move. On August 1, 2026, the Mariners traded the veteran right-hander to the Chicago White Sox, ending his four-season run in Seattle just three days before Major League Baseball’s August 3, 2026 trade deadline.
Trade Details: What Seattle Received for Luis Castillo
According to ESPN’s Jeff Passan, the Mariners and White Sox agreed to a deal sending Castillo to Chicago in exchange for right-handed relief pitcher Seranthony Dominguez, outfielder Nolan Jones, and catching prospect Boston Smith. ESPN’s Alden Gonzalez reported that the White Sox agreed to take on the entirety of the money remaining on Castillo’s contract, giving the Mariners significant payroll relief.
The move addresses two needs Seattle had signaled all season: bullpen depth and offensive help. Dominguez gives the Mariners a proven right-handed reliever, while Jones adds a bat to the lineup. Smith joins the organization as a catching prospect for the future.
Why the White Sox Wanted Luis Castillo
Chicago entered deadline week looking to bolster its starting rotation while trying to protect a lead in the American League Central. Adding a durable, experienced arm like Castillo, who has a track record as one of MLB’s most reliable innings-eaters over the past several seasons, gives the White Sox rotation depth for a playoff push down the stretch of the 2026 season.
A Difficult Contract Year for Castillo in Seattle
The trade comes after a rough statistical season for the 33-year-old. Castillo entered deadline week with roughly a 5.06 ERA and a 1.40 WHIP over 20 appearances (17 starts), numbers well below his career norms. Reports throughout July from outlets including MLB.com and MLB Trade Rumors indicated the Mariners were actively fielding calls on Castillo, along with fellow starter Emerson Hancock and outfielder Randy Arozarena, as Seattle looked to reshape its roster for a playoff push in the weak AL West.
Castillo was owed roughly $22.75 million in each of the 2026 and 2027 seasons, with a $25 million vesting option for 2028 tied to an innings threshold. That salary, paired with his statistical decline, had made him a tricky trade chip for much of the summer. Ultimately, the White Sox absorbing the full remaining money cleared the path for the deal to get done.
Luis Castillo’s Career Background
Born December 12, 1992, in BanÃ, Dominican Republic, Castillo made his MLB debut in 2017 with the Cincinnati Reds. He was traded to Seattle at the 2022 trade deadline and signed a five-year, $108 million extension with the Mariners shortly after, a deal that made him a key part of the franchise’s rotation for the past several seasons.
A three-time All-Star (2019, 2022, 2023), Castillo built a reputation in Seattle as “La Piedra” (The Rock) for his durability and consistency. His 3.46 ERA in a Mariners uniform ranks among the best in franchise history. He enters this new chapter of his career with the White Sox looking to help stabilize a playoff-contending rotation in Chicago.
What This Means for the Mariners
Seattle’s rotation, long considered one of the deepest in baseball, now leans further on younger arms like Logan Gilbert, Bryan Woo, George Kirby, and Bryce Miller, along with Hancock. Mariners baseball operations president Jerry Dipoto had said throughout the year that trading a starter would only happen if it addressed the team’s clear needs for right-handed hitting and bullpen help, and Saturday’s deal reflects that stated priority.
Stay tuned as more trade deadline reactions and grades roll in over the next 48 hours!