White Sox Acquire Luis Castillo from Mariners

In exchange, the White Sox sent reliever Seranthony Domínguez, outfielder Nolan Jones, and catching prospect Boston Smith to Seattle. Chicago is also absorbing the remaining money on Castillo’s contract, which includes the rest of 2026 and $22.75 million for 2027, with a potential vesting option for 2028.

Castillo, 33, is a three-time All-Star who has struggled this season with a 3-9 record and 5.06 ERA over 99.2 innings (17 starts). The move adds a veteran arm with postseason experience to a White Sox rotation that has been thin beyond its top options.

The White Sox entered the deal as the surprise leaders of the AL Central and were no doubt looking to reinforce their pitching staff ahead of the trade deadline. Castillo provides innings and a track record of success, even if his current form isn’t what it once was.

For the Mariners, the trade sheds some salary and a surplus starter while adding some bullpen help and a catching prospect as they evaluate their direction with a sub-.500 record just days before the deadline.