Thompson, ranked No. 123 in the 2018 recruiting class, chose to switch sides in the Red River Rivalry and committed to the Longhorns over North Carolina and Miami.
Thompson plays at Southmoore High School in Moore, Oklahoma, located 13 miles from the University of Oklahoma campus in Norman. His father played for the Sooners from 1986-88 and Thompson's brother, Kendal, also played quarterback at Oklahoma before finishing his career at Utah. Kendal Thompson is currently a wide receiver for the NFL's Washington Redskins.
Casey Thompson, a 6-foot-1, 190-pound dual-threat passer, is a significant addition for new Texas coach Tom Herman, who now has three verbal commitments for the 2018 class. Thompson will graduate in December and enroll early next spring at Texas. Sophomore Shane Buechele and freshman Sam Ehlinger are the only scholarship QBs on the roster this spring.
Thompson has thrown for more than 6,500 yards and rushed for more than 2,000 yards with 109 career touchdowns going into his senior year.
He had an Oklahoma hat on the table at his commitment ceremony, but the Sooners had already taken a 2018 QB commitment last August from Cameron Rising, the No. 106 recruit in the ESPN Junior 300 out of Newbury Park, California.