Upadacitinib in Giant Cell Arteritis (GCA) With Active Large-vessel Involvement.

This is an observational, multicenter cohort evaluating the safety and efficacy of upadacitinib in patients with giant cell arteritis (GCA). Patient treatment and follow-up will be conducted in accordance with routine clinical care. No additional visits or examinations will be added for the purposes of the study. Participants will be followed as part of the usual management of their disease. No modifications will be made (no additional visits, examinations, or questionnaires). The safety and well-being of participants will therefore remain unchanged. The participant will be informed about the study during one of their routine care visits. The information will be provided by the investigator, and the participant's non-opposition to participation in the study will be obtained. Patients will then be followed and managed according to routine care (visits and examinations). Routine care includes: * A clinical assessment of efficacy and safety at weeks 12, 24, 36, 52, and 104; * Oral prednisone treatment at the initial doses recommended by international and French guidelines, in accordance with routine care. Treatment with upadacitinib will be initiated at the time of patient inclusion (one 15 mg tablet per day) and will be maintained for 104 weeks. Data will then be collected from the participant's medical record (including medical reports, original laboratory test results, imaging reports and medical examinations, and nursing records) for the period of participation in the research, solely for the purpose of meeting the objectives of the research. Clinical, biological, and radiological efficacy data, as well as treatment safety, will be prospectively analyzed at 3, 6, 12, and 24 months.