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.