This study is for people with sickle cell disease (SCD), a condition that affects red blood cells. We are testing a medicine called osivelotor to see if it is safe and works well. **Phase 2/3** means we are in the middle stages of testing. The study has three parts:

**Part A:** Tests osivelotor's safety and effectiveness in adults to find the best dose.

**Part B:** Compares osivelotor to a placebo (a pill without medicine) in adults and teens with SCD for 48 weeks.

**Part C:** Looks at how osivelotor behaves in the body and its safety in children.

Key Points:

• The study may last up to 48 weeks.
• Participants must have stable health and not be pregnant or breastfeeding.
• Regular visits are needed, and there might be compensation for participation.

To join, you should have 2 to 10 sickle cell crises in the past year and meet other health requirements. You cannot join if you've had more than 10 crises, are pregnant, or have had recent blood transfusions or hospitalizations for sickle cell issues.