A Study to Evaluate the Safety and Effectiveness of Upadacitinib Tablets in Adult and Adolescent Participants With Severe Alopecia Areata

Inclusion Criteria: * Adult individuals must be \< 64 years old at Baseline Visit. Where permitted outside United States (US)/European Union (EU), adolescent individuals who are at least 12 years old at Screening may participate in Study 1 and Study 2. Adolescent individuals in the US who are at least 12 years old at Screening may participate in Study 4. * Diagnosis of severe alopecia areata (AA) with Severity of Alopecia Tool (SALT) score \>= 50 scalp hair loss at Screening and Baseline. * Severe AA with no spontaneous scalp hair regrowth over the past 6 months. * Current episode of AA of less than 8 years. Exclusion Criteria: * Current diagnosis of primarily diffuse type of AA. * Current diagnosis of other types of alopecia that would interfere with evaluation of AA, including but not limited to female pattern hair loss, male pattern hair loss (androgenetic alopecia) Stage III or greater based on Hamilton-Norwood classification, traction alopecia, lichen planopilaris (LPP), discoid lupus, frontal fibrosing alopecia (FFA), central centrifugal cicatricial alopecia (CCCA), folliculitis decalvans, trichotillomania, and telogen effluvium. * Diagnosis of other types of inflammatory scalp, eyebrow, or eyelash disorders that would interfere with evaluation of AA as determined by the investigator, including but not limited to seborrheic dermatitis, scalp psoriasis, atopic dermatitis (AD), and tinea capitis.