Description: Upadacitinib, also known as ABT-494, is a potent and selective JAK inhibitors in development for rheumatoid arthritis. ABT-494 is approximately 74 fold selective for Jak1 over Jak2 in cellular assays dependent on specific, relevant cytokines. ABT-494 demonstrates efficacy in rat arthritis models. Preliminary evidence suggests that compared to tofacitinib, ABT-494 may spare Jak2 and Jak3 dependent signaling.