Kirby will join the Mariners' major-league roster shortly, Jeff Passan of ESPN.com reports.
The Mariners already called up one prospect straight from Double-A this season, but the Matt Brash experiment ended when the rookie was optioned Thursday after struggling to a 7.65 ERA in five starts. The Mariners will hope for better from Kirby, and there's reason to believe they'll get it, as Kirby doesn't have anywhere near Brash's command issues. Command is instead Kirby's calling card, as the 2019 first-rounder has walked just 4.4 percent of the batters he's faced in his minor-league career. Pair that with his 30.0 percent strikeout rate and there's plenty of reason to get excited, though he'll still have to navigate a big step up in competition. Kirby is expected to start Sunday against the Rays, per Jonathan Mayo of MLB.com, so it's likely the transaction won't become official until then.