Mariners trade Luis Castillo to White Sox for 3 players, including Seranthony Domínguez

Adam Jude, The Seattle Times on Aug 1, 2026

Published in Baseball

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SEATTLE — The Mariners have made their first meaningful move of the summer trade season, and it’s the one move they had hoped to make all along.

Veteran right-hander Luis Castillo has been traded to the Chicago White Sox for three players, an industry source with knowledge of the deal confirmed Saturday afternoon.

The White Sox will absorb the entirety of Castillo’s contract, roughly $30 million through the 2027 season. The 33-year-old right-hander also has a vesting option worth $25 million for 2028 if he reaches 180 innings next season.

In return, the Mariners are acquiring veteran right-handed reliever Seranthony Domínguez, veteran outfielder Nolan Jones and Double-A catching prospect Boston Smith.

Four years ago, Castillo became one of the best trade-deadline acquisitions in Mariners history, coming over from Cincinnati in a five-player deal. The Mariners signed him to a five-year, $108 million contract extension shortly after the trade, and he was instrumental in helping the Mariners end a 21-year playoff drought in 2022.

Castillo was as consistent as any pitcher in the AL during his three full seasons in Seattle, posting a 3.46 ERA with 633 strikeouts in 618 innings in his first 106 starts with the Mariners. He was an All-Star for the Mariners in 2023 — at T-Mobile Park — finishing the year with a 14-9 record, a 3.34 ERA and 219 strikeouts in 197 innings.

This year, Castillo’s production dropped off considerably in April and May, and despite being the highest-paid player on the roster he effectively became the No. 6 starter in the Mariners’ six-man rotation.

He’ll now slot into the middle of the rotation for a young White Sox club vying for the AL Central title.

Domínguez, 31, is a veteran of eight major league seasons, and he’s in the first year of a two-year, $20 million deal he signed with the White Sox last winter. He’s scheduled to make $10.5 million in 2027, which the Mariners will take on.

Of note, Domínguez was pitching for the Toronto Blue Jays last fall when he surrendered the go-ahead, eighth-inning grand slam to the Mariners’ Eugenio Suarez in Game 5 of the American League Championship Series at T-Mobile Park.

He’ll now pitch regularly for the Mariners.

Domínguez has a 4.10 ERA with 12 saves in 42 appearances for the White Sox this season. He’ll line up in a high-leverage role out of Seattle’s bullpen, but he’s not expected to supplant Andrés Muñoz as the Mariners’ closer.