A Study to Evaluate the Safety and Efficacy of Upadacitinib in Participants With Giant Cell Arteritis

This study consists of two periods. The objective of Period 1 is to evaluate the efficacy of upadacitinib in combination with a 26-week corticosteroid (CS) taper regimen compared to placebo in combination with a 52-week CS taper regimen, as measured by the proportion of participants in sustained remission at Week 52, and to assess the safety and tolerability of upadacitinib in participants with giant cell arteritis (GCA). The objective of Period 2 is to evaluate the safety and efficacy of continuing versus withdrawing upadacitinib in maintaining remission in participants who achieved sustained remission in Period 1.