The White Sox are acquiring right-hander Luis Castillo in a trade with the Mariners for reliever Seranthony Domínguez, outfielder Nolan Jones and catching prospect Boston Smith, a source told MLB.com’s Mark Feinsand. The clubs have not confirmed the move.
Regardless of how or when his Mariners tenure ended, Castillo has been a defining piece to Seattle’s success of this era — and his acquisition from the Reds in the 2022 Deadline blockbuster remains one of the biggest trades in franchise history.
It wouldn’t be a stretch to say that transaction represented the moment that their rebuild ended, as he immediately ascended to the top of their rotation and helped the club snap a 21-year playoff drought.
Now in his age-33 season, Castillo has lost a bit of that elite stuff — but he’s still remained a workhorse, logging at least 175 innings and 30 starts from 2023-25, his three full seasons in Seattle.
That said, he’s experienced more volatility in ‘26, with a 5.06 ERA and 78 ERA+ (league average is 100) in 20 outings (17 starts). Some of those numbers were compounded by a rough, nine-start stretch to begin the year, which led to him being piggybacked with Bryce Miller for four starts from mid-May to mid-June.
Part of the calculus to do so, instead of moving Castillo to the bullpen permanently, was to keep him stretched out for this precise moment — as his trade value would’ve tanked had he been a reliever’s routine. There’s also the fact that he was the Mariners’ most expensive player and the pitching staff’s elder statesman.
Seattle had been actively listening on Castillo and Emerson Hancock for much of the past few weeks, and their preference had been to deal the veteran, who is owed roughly $30 million through next season and has a $25 million vesting option for 2028 if he accumulates 180 innings in ‘27.
That seemingly made the market for Castillo, 34, more limited than Hancock, 27, who is earning the league minimum (just under $800,000) and is under club control through 2030.
The Mariners had been more open to deal one or the other but not both, which itself represented a philosophical shift, as they had adamantly avoided dealing from their rotation since emerging from their rebuild late in 2021.
But with No. 2 prospect Kade Anderon expected to be part of their permanent plans as soon as 2027, and potentially sooner for a playoff push, and No. 3 prospect Ryan Sloan not far behind, they were willing to deal from their big league depth to bolster the rest of the roster.
