Objective We examine coverage of self‐administered disease‐modifying antirheumatic drugs (DMARDs) in Medicare Part D. Methods Using 2022–2026 Part D formulary data, we assessed coverage of the following DMARD classes that treat relapsed rheumatoid arthritis (RA): tumor necrosis factor (TNF) inhibitors, T cell costimulatory modulator, interleukin‐6 (IL‐6) inhibitors, and JAK inhibitors. We measured (1) coverage of individual DMARDs and (2) the generosity of coverage between classes (the share of plans covering at least one drug in each class) and within classes (the share of covered drugs within each class). Results We included 26,915 plan‐year observations, representing 217.6 million enrolled beneficiaries from 2022 to 2026. In the five‐year period, coverage was relatively complete (>94%) for etanercept and adalimumab (TNF inhibitors) and upadacitinib (JAK inhibitor). However, coverage was lower for golimumab and certolizumab (TNF inhibitors), abatacept (the sole T cell costimulatory modulator), sarilumab (IL‐6 inhibitor), and baricitinib (JAK inhibitor). Moreover, only 10.4% and 37.6% of stand‐alone and Medicare Advantage (MA) Part D plans, respectively, covered all mechanisms of action, mostly due to low coverage of abatacept. In 2026, only 0.3% and 21.2% of stand‐alone and MA Part D plans, respectively, covered abatacept. On the other hand, coverage increased for IL‐6 inhibitors, likely due to the availability of biosimilar drugs for tocilizumab in 2024. Conclusion The growing exclusions of self‐administered DMARDs across several mechanisms of action and heterogeneity in coverage by plan type suggest potential barriers to accessing optimal RA treatments. Further monitoring of formulary adequacy and research into the clinical impacts of formulary exclusions are warranted.