Quinn Costello is a 6-10 stretch power forward from The Newman School in Boston, Massachusetts, who came off the bench as a junior during Newman's NEPSAC AAA championship run before breaking out in the summer of 2025 with the Middlesex Magic on the Under Armour circuit. He earned co-Most Outstanding Player at Pangos All-American Camp and averaged 16.4 points, 8.1 rebounds, and 2.0 assists as a senior. A McDonald's All-American with a soft shooting touch and elite floor-spacing ability, Costello committed to Michigan in September 2025 under coach Dusty May.