Modern New Guineans carry 50,000-year-old genetic diversity from Sahul settlement. 58 new PNG genomes fill sampling gaps for migration models. One or two Wallacea migrations to northeast Sahul both match data. Ancestral New Guinean and Australian groups diverged early in Wallacea via northern route. Earliest Sahul era featured gene flow between already differentiated groups. All modern New Guineans, Bismarck islanders, and Australians descend from these groups. New Guinea settlement started in southeast with oldest sites. Southeast origin led to two migrations into south and north lowlands. Lowland migrations reached west and east highlands. Ancient gene flows linked New Guinea, Australia, East Indonesia, and Bismarck Archipelago. Early Sahul was dynamically interactive, not isolated.