To Assess the Efficacy, Safety, and Tolerability of INCB000928 in Participants With Fibrodysplasia Ossificans Progressiva

Inclusion Criteria: * Female and male participants: * Cohort 1: ≥ 12 years of age. * Cohort 2: 6 to \< 12 years of age. * Cohort 3: 2 to \< 12 years of age (after eDMC review of safety data from Cohort 2). * Clinical diagnosis of FOP. * Willingness to avoid pregnancy or fathering children based on the criteria below. * Willing and able to undergo low-dose WBCT (excluding the head) imaging without requiring intubation. * Further inclusion criteria apply. Exclusion Criteria: * Pregnant or breast-feeding. * CAJIS score ≥ 24. * FOP disease severity that in the investigator's opinion precludes participation. * Any clinically significant medical condition other than FOP that would, in the investigator's judgment, interfere with full participation in the study, pose a significant risk to the participant, or interfere with interpretation of study data. * Chronic or current active infectious disease requiring systemic antibiotic, antifungal, or antiviral treatment. * HIV, HBV, or HCV infection. Note: * Further exclusion criteria apply.