Abstract Since January 2020, Medicare has covered opioid use disorder (OUD) treatment services at opioid treatment programs (OTPs), the only outpatient settings allowed to dispense methadone for treating OUD. This study examined policy-associated changes in Medicare acceptance and the availability of four OUD treatment services (ongoing buprenorphine, HIV/AIDS education, employment services, and comprehensive mental health assessment), by for-profit status, and county-level changes in Medicare-accepting-OTPs access, by sociodemographic characteristics (racial composition, poverty rate, and rurality). Using data from the 2019-2022 National Directory of Drug and Alcohol Abuse Treatment Facilities, we found Medicare acceptance increased from 21.31% in 2018 to 80.76% in 2021. The availability of the four treatment services increased but no increases were significantly associated with Medicare coverage. While county-level OTP access significantly improved, counties with higher rates of nonwhite residents experienced an additional average increase of 0.86 Medicare-accepting-OTPs (95% CI: [0.05, 1.67]) compared to those without higher rates of nonwhite populations. Overall, Medicare coverage was associated with improved OTP access, not ancillary services.