A Phase 3 Study to Compare Upadacitinib to Abatacept in Subjects With Rheumatoid Arthritis on Stable Dose of Conventional Synthetic Disease- Modifying Antirheumatic Drugs (csDMARDs) Who Have an Inadequate Response or Intolerance to Biologic DMARDs

Main Inclusion Criteria: * Diagnosis of rheumatoid arthritis (RA) for ≥ 3 months who also fulfill the 2010 American College of Rheumatology (ACR)/European League Against Rheumatism (EULAR) classification criteria for RA * Participants have been treated for ≥ 3 months prior to the screening visit with ≥ 1 bDMARD therapy, but continue to exhibit active RA or had to discontinue due to intolerability or toxicity, irrespective of treatment duration and have never received abatacept prior to the first dose of study drug * Participants have been receiving csDMARD therapy ≥ 3 months and on a stable dose for ≥ 4 weeks prior to the first dose of study drug. The following csDMARDs are allowed: methotrexate (MTX), sulfasalazine, hydroxychloroquine, chloroquine, and leflunomide. A combination of up to two background csDMARDs is allowed except the combination of MTX and leflunomide * Meets the following criteria: ≥ 6 swollen joints (based on 66 joint counts) and ≥ 6 tender joints (based on 68 joint counts) at Screening and Baseline Visits and high-sensitivity C-reactive protein (hsCRP) ≥ 3 mg/L at Screening Main Exclusion Criteria: * Prior exposure to any Janus kinase (JAK) inhibitor (including but not limited to upadacitinib, tofacitinib, baricitinib and filgotinib) * Prior exposure to abatacept * History of any arthritis with onset prior to age 17 years or current diagnosis of inflammatory joint disease other than RA. Current diagnosis of secondary Sjogren's Syndrome is permitted * Laboratory values meeting the following criteria within the Screening period prior to the first dose of study drug: serum aspartate transaminase \> 2 × upper limit of normal (ULN); serum alanine transaminase \> 2 × ULN; estimated glomerular filtration rate by simplified 4-variable Modification of Diet in Renal Disease formula \< 40 mL/minute/1.73 meter (m)\^2; total white blood cell count \< 2,500/ μL; absolute neutrophil count \< 1,500/μL; platelet count \< 100,000/μL; absolute lymphocyte count \< 800/μL; and hemoglobin \< 10 g/dL