At this time, Ieyasu sent a letter to Masamune indicating the reward of a new, additional territory of 490,000 koku value on top of his existing 580,000 koku upon victory ("Assurance of Hyakumangoku [1 million koku]" owned by the Sendai City Museum).
この際、家康は政宗に、戦勝の暁には現在の所領58万石に加え、新たに49万石の領土を与えるという内容の書状（「百万石のお墨付き」仙台市博物館・蔵）を送っている。