Subjects in CR1 will be approached for this study after induction/consolidation therapy is complete and a decision not to proceed with transplantation is made or a suitable donor could not be identified. Subjects will be randomized in a 2:1 ratio to receive gilteritinib or placebo. Subjects will enter the screening period up to 14 days prior to the start of treatment. Subjects will be administered treatment over continuous 28-day cycles. After treatment discontinuation, subjects will have a 30-day follow-up visit for safety, after which the subjects will enter the long-term follow up period for collection of subsequent AML treatment, remission status, and survival (cause of death and date of death). Gilteritinib or placebo will be given daily for up to 2 years. Subjects will be followed for up to 3 years from the subjects 30-day follow up, or until 80% of the subjects have an RFS event, whichever comes first. Study drug will not be provided during the follow-up period.