The Rays promoted Gillen from High-A Bowling Green to Double-A Montgomery on Sunday, Marc Topkin of the Tampa Bay Times reports.
Gillen will move up to Double-A after slashing .342/.449/.589 with 12 home runs and 28 stolen bases over 265 plate appearances in 57 games with Bowling Green. The 20-year-old is considered to be one of Tampa Bay's top overall prospects, and he'll have a shot to climb to the Triple-A level before the end of 2026.