Grimes announced the commitment during a press conference at his high school.
In the past week, Kansas head coach Bill Self and Texas head coach Shaka Smart came by to make late pitches.
Grimes, a 6-foot-5 combo guard from The Woodlands College Park High School (Texas), is ranked No. 13 in the ESPN 100 for the 2018 class. He slots in as the No. 3 shooting guard in the country, but he can play both guard positions.
"One of the things that's really good about him is his versatility," Rhossi Carron, Grimes' AAU coach, told ESPN. "At 6-5, 205 pounds, he can guard point guards and shooting guards. And since everyone's going small, he can probably guard small forwards in college. He doesn't have to have the ball to be successful. But if he does have the ball, he can make plays, he can run a team. He'll be fine alongside another point guard."
Playing for Basketball University on the Adidas Gauntlet circuit, Grimes averaged 16.6 points, 5.7 rebounds and 2.7 assists over the spring and summer, shooting 40.0 percent from 3-point range. He had one of the best performances of July, when he scored 41 points against Team Arsenal, going 16-from-23 from the field and 7-for-12 from behind the arc.
"I think immediately he's going to be able to score the ball," Carron said. "Because of his versatility, he's going to find his way on the floor. He can play with the ball, score and make other guys better. His ability to make shots is really important. That's the new age of basketball -- spreading the floor, guys are making plays. He's gotten unbelievably better.
"I think the thing he's improved on the most is playing with better pace and being able to leave his imprint on the game. Being able to dominate games and being able to play faster. Those things are going to be really important to him at the next level."
Grimes is the fourth top-35 prospect to commit to Kansas in the 2018 class, joining point guard Devon Dotson (No. 26), power forward Silvio De Sousa (No. 28) and center David McCormack (No. 33). The Jayhawks are still involved with top uncommitted prospect Zion Williamson (No. 2), and they recently made the final three for Romeo Langford (No. 5).
Self had a top-five recruiting class going into Wednesday and will jump into the top two with the addition of Grimes.