The Mariners promoted Kirby from High-A Everett to Double-A Arkansas on Tuesday, Cameron Van Til of the Everett Herald reports.
Kirby had been sidelined for most of the past month at Everett due to right shoulder fatigue, but he was cleared to make his final start with the affiliate Saturday, when he tossed three shutout innings. Along with Kirby, the Mariners also promoted one of their other top pitching prospects in Emerson Hancock to Double-A Arkansas. Kirby finishes his time at Everett with a 2.38 ERA, 1.00 WHIP and 52:8 K:BB across 41.2 innings.