The Seattle Mariners have two new players on their big league roster after the MLB trade deadline, plus the expected return of Brendan Donovan this week.

Kalshi’s extended promo with code OREGONLIVE1 offers new users up to $500 bonus credit for trading on MLB Mariners-Tigers markets after the trade deadline.

Bullpen inflexibility was a problem for the Mariners at the beginning of the season, and it's going to rear itself here at the trade deadline as well.

A look at how the 2026 MLB trade deadline shook out for the Seattle Mariners' AL West rivals, including the first-place Houston Astros.

SEATTLE – The Twins are a team that won’t go down without a fight, as evidenced by their 7-6 walk-off loss to the Seattle Mariners on Sunday at T-Mobile Park, but there are two key numbers to remember entering Monday’s MLB trade deadline: Four and one.

The Seattle Mariners traded right-handed pitcher Luis Castillo to the Chicago White Sox in exchange for right-handed reliever Seranthony Domínguez, outfielder Nolan Jones, and catcher prospect Boston Smith.

The Mariners needed to get out from Luis Castillo's salary any way they could. They managed to add a prospect while doing it. Alika Jenner / The Athletic has live coverage of the 2026 MLB Trade Deadline.