Number of adult participants with change from baseline in hemoglobin (Hb) through week 12 as measured by change in osivelotor concentrations from baseline or percentage change from baseline of clinical measures of anemia Hb and hemolysis (including indirect bilirubin, reticulocytes and lactate dehydrogenase).

Co-primary endpoints: Hb response (increase from baseline of \>1 g/dL) at Week 48 (based on average of Hb levels at Week 40 and Week 48) and the Annualized rate of VOC through end of Week 48. A VOC is defined as an acute episode of pain that: * Has no medically determined cause other than a vaso-occlusive event, and * Results in a visit to a medical facility (hospitalization, emergency department, urgent care center, outpatient clinic, or infusion center), and * Requires parenteral narcotic agents, parenteral nonsteroidal anti-inflammatory drugs (NSAIDs), or an increase in treatment with oral narcotics. Complicated VOCs of acute chest syndrome (ACS), hepatic sequestration, splenic sequestration, priapism, and dactylitis that meet the requirements listed above will be included in this co-primary endpoint.

Incidence of Treatment Emergent Adverse Events: * Incidence of SAEs * Incidence of AEs leading to discontinuation * Change from baseline in laboratory parameters.

Mouth feel visual analogue scale (VAS) assesses the participant's global perception of mouth feel (that is, effects over the whole course of the drug experience including any carryover effects). A 100-point VAS is used to assess response based on a score ranging from 0 points to 100 points (0 points = " Bad Mouth feel ", 50 points = "neither bad nor good mouth feel", and 100 points = "Good Mouth feel ").

Bitter visual analogue scale (VAS) assesses the participant's global perception of bitterness (that is, effects over the whole course of the drug experience including any carryover effects). A 100-point VAS is used to assess response based on a score ranging from 0 points to 100 points (0 points = " extremely bitter ", 50 points = "neither bad nor good bitterness", and 100 points = "not bitter").

Tongue/mouth burn visual analogue scale (VAS) assesses the participant's global perception of tongue/mouth burn (that is, effects over the whole course of the drug experience including any carryover effects). A 100-point VAS is used to assess response based on a score ranging from 0 points to 100 points (0 points = "extreme burn", 50 points = "neither bad nor good burn", and 100 points = "no burn").

Overall liking visual analogue scale (VAS) assesses the participant's global perception of overall liking (that is, effects over the whole course of the drug experience including any carryover effects). A 100-point VAS is used to assess response based on a score ranging from 0 points to 100 points (0 points = "bad", 50 points = "neither bad nor good", and 100 points = "good").

AUC from 0 to 144 hours is a measure of the whole blood concentration of the drug over time. It is used to characterize drug absorption; if AUC0-144 not available, then AUClast will be calculated.