This study will be conducted to assess the safety and pharmacokinetics of INCB123667 when administered orally to adult participants with moderate or severe hepatic impairment.

Inclusion Criteria:

• Ability to comprehend and willingness to sign a written ICF for the study.
• Aged 18 to 80 years, inclusive, at the time of signing the ICF.
• Moderate or severe hepatic impairment based on CP score.
• Medical findings consistent with the degree of hepatic dysfunction, determined by medical history, physical examination, vital sign measurements, 12-lead ECGs, and clinical laboratory determinations at screening or check-in (as applicable). Participants with abnormal findings considered not clinically significant by the medical monitor or investigator are eligible.
• Body mass index of 18.0 to 43.0 kg/m2 (inclusive).
• Willingness to avoid pregnancy or fathering children.

Exclusion Criteria:

• Participants who have a current, functioning organ transplant or are on the national transplant list and expected to receive a transplant within 3 months.
• Tobacco or nicotine-containing product use of > 10 cigarettes per day within 1 month before screening.
• Participants who had a change in disease status within 30 days before screening, as documented by the participant's medical history, that is deemed clinically significant by the investigator.
• Participants who have a history of paracentesis within 2 months prior to check-in.
• Participants who required new medication or an increase in dose for hepatic encephalopathy within 3 months prior to check-in.
• Participants who have a history of unstable diabetes mellitus (as evidenced by hemoglobin A1c ≥ 10.0%). Medications for treatment of diabetes mellitus must be reviewed and approved by the investigator and medical monitor. Participants who have a portal systemic shunt. Up to 3 participants with transjugular intrahepatic portosystemic shunt may be included.
• Participants who had esophageal banding within 3 months prior to check-in or required any other treatment for gastrointestinal bleeding within 6 months prior to check-in.

Other protocol-defined Inclusion/Exclusion Criteria may apply.