This randomized Phase 3 open-label study will compare the efficacy of the T-cell immunoglobulin and immunoreceptor tyrosine-based inhibitory motif (ITIM) domain (TIGIT) monoclonal antibody domvanalimab, the anti programmed cell death protein 1 (PD-1) monoclonal antibody zimberelimab, and multiagent chemotherapy versus the anti PD-1 monoclonal antibody nivolumab and multiagent chemotherapy in the first-line treatment of participants with locally advanced unresectable or metastatic gastric, gastroesophageal junction (GEJ), and esophageal adenocarcinoma.