This is a Phase 3, 2-arm, randomized, open-label, global, multicenter study comparing the efficacy of ripretinib to sunitinib in participants with GIST who progressed on first-line treatment with imatinib, harbor co-occurring KIT exons 11+17/18 mutations, and are without KIT exon 9, 13, or 14 mutations. Upon disease progression as determined by an independent radiologic review, participants randomized to sunitinib will be given the option to either crossover to receive ripretinib 150 mg QD or discontinue sunitinib.