This is a Phase 3 multicenter study with 2 periods. Period 1 was a 24-week, randomized, double-blind, parallel-group, active-controlled period designed to compare the safety and efficacy of upadacitinib 15 mg and abatacept for the treatment of signs and symptoms of participants with moderately to severely active RA who had an inadequate response to or intolerance to bDMARD therapy and were currently on a stable dose of csDMARD(s) and had never received abatacept. Period 2 is an open-label, long-term extension study to evaluate the long-term safety, tolerability, and efficacy of upadacitinib 15 mg once a day (QD) in participants with RA who had completed Period 1.