The Guardians promoted Hartle to Double-A Akron on Thursday.
Hartle had played his entire 2025 season with High-A Lake Country prior to Thursday's promotion. He posted a 2.35 ERA with an 100:37 K:BB across 103.1 innings in 22 starts. The 22-year-old did not allow any earned runs in his last six starts since July 12, which included 28 strikeouts in 31 innings.