The Guardians selected Peterson's contract from Triple-A Columbus on Tuesday, Zack Meisel of The Athletic reports.
Peterson struggled a bit after being promoted to Triple-A in June, posting a 4.27 ERA and 1.37 WHIP across 90.2 innings compared to the 1.47 ERA and 0.82 WHIP he held in 55 frames at Double-A Akron. The 26-year-old's addition to the 40-man roster will prevent him from being selected in the Rule 5 Draft, but the Guardians will likely keep him in Triple-A to begin the 2026 campaign.