Kirby has been hitting the upper 90s with his fastball during simulated games at the Mariners' alternate training site in Tacoma, Shannon Drayer of 710 ESPN Seattle reports.
The news comes via general manager Jerry Dipoto, who relayed updates on several of the organization's top prospects during a radio interview Thursday. Kirby was impressive at short-season Everett last season (2.35 ERA, 25:0 K:BB across 23 innings) after his selection in the first round of the first-year player draft, and with no minor-league season this year, he's at least getting valuable development time in at Tacoma.