A Study of LY4005130 in Adult Participants With Severe Alopecia Areata (Hair Loss)

Inclusion Criteria: * Have severe Alopecia Areata (AA) that meets all of the following criteria: * Hair loss encompassing ≥50% and ≤90% of the scalp, as measured by Severity of Alopecia Tool (SALT) score * The duration of the current episode of severe AA is at least 6 months and does not exceed 4 years * No significant spontaneous hair regrowth in the investigator's opinion for at least 6 months * Agree not to use any AA treatments during the study Exclusion Criteria: * Primarily "diffuse" type of AA (characterized by diffuse hair shedding) * Are currently experiencing other forms of alopecia * Participants who, in the opinion of the investigator, are currently experiencing or have a history of unstable concomitant disease that requires frequent hospitalizations, and/or frequent use of systemic immunosuppressants that may interfere with participation in the study * Have had any major surgery within 8 weeks prior to screening or will require major surgery during the study * Have a history or presence of cardiovascular, respiratory, hepatic, gastrointestinal, endocrine, hematological, neurological, or neuropsychiatric disorders or any other serious and/or unstable illness