The move to the Air Force Academy is Stubblefield's 12th in 16 years.
Under the non-exclusive tag, other teams are able to negotiate a contract with Barkley, though the Giants can still match any offer.
Joey Porter Jr. and Brenton Strange impressed at the 2023 NFL Scouting Combine.
The Philadelphia native is the fourth player to join the Nittany Lions' Class of 2024.
Quarterback Beau Pribula and linebacker Tony Rojas were among the newcomers who made the strongest impression this winter.
On the last day of winter workouts, the Nittany Lions took to the weight room to flex their muscles.