A Phase 2/3 Randomized, Multicenter Study of Osivelotor Administered Orally to Participants with Sickle Cell Disease and an Open-Label Pharmacokinetics Study in Pediatric Participants with Sickle Cell Disease

Inclusion Criteria: Part A, Part B, and OLE: - Male or female with SCD - Participants with stable Hb value as judged by the Investigator - For participants taking hydroxyurea and/or L-glutamine, the dose must be stable for at least 90 days prior to signing the ICF or assent and with no anticipated need for dose adjustments during the study in the opinion of the Investigator. Part B: - Participants with SCD ages 12 to 65 years, inclusive - Participants with more than or equal to 2 and ≤ 10 VOCs within 12 months of Screening. OLE: - Participants who have completed the Part B will be eligible. Exclusion Criteria: Part A, Part B, and OLE: - Participants who had more than 10 VOC within 12 months of screening - Female participant who is breastfeeding or pregnant - Participants who receive RBC transfusion therapy regularly or received an RBC transfusion ---for any reason within 90 days of Day 1 - Participants hospitalized for sickle cell crisis or other vaso-occlusive event within 14 days of signing the ICF or anytime during the screening period.