A Study in Young People and Adults to Learn About the Medicine Ritlecitinib for Treatment of Patchy Hair Loss, Known by the Medical Term as Moderate Alopecia Areata

Key Inclusion Criteria * 18 years or older (or the minimum age of consent in accordance with local regulations) at screening. Adolescents (12 to \<18 years of age at screening) are also eligible for this study, but only if permitted by the local IRB/EC and local regulatory health authority (if applicable). Where these approvals have not been granted, only participants 18 years of age and older at screening will be enrolled * Have a clinical diagnosis of AA with no other etiology of hair loss. * Have \>20% to \<50% hair loss of the scalp, as measured by SALT. * Current AA episode of hair loss ≥6 months and ≤10 years (Current episode is defined as the continuous period of AA-related scalp hair loss since the last time the subject had no visible scalp patches). Key Exclusion Criteria 1\. Diseases or conditions affecting hair loss, including: * Other types of alopecia (including, but not limited to, traction and scarring alopecia, telogen effluvium). Participants with androgenetic alopecia will be excluded. * Other scalp disease that may impact AA assessment (eg, scalp psoriasis, dermatitis, etc.). * Active systemic diseases that may cause hair loss (eg, lupus erythematosus, thyroiditis, systemic sclerosis, lichen planus, etc).