Young originally committed to the Trojans in July. He's the fourth-ranked dual-threat quarterback in his class and the No. 88 overall prospect in the ESPN 300.
"I'd like to say a huge thank you to coach Helton, coach Harrell, Gavin, coach Colbert, the rest of the USC staff for the opportunity that they have given me," he said in a statement. "I would also like to thank the USC fans and community for all of the support. I will always have love for the University of Southern California, and wish for nothing but the best for its players, coaching staff, and fans."
Young was the highest-ranked recruit in USC's 2020 class. Clay Helton's squad does not currently have any other commitments ranked in the top 300.
Alabama, meanwhile, has now secured 10 recruits from next year's top 100 prospects. Young could potentially be a big piece of the Crimson Tide's offense as Tua Tagovailoa is expected to declare for the NFL draft.