This study explored how access to medication for opioid use disorder (MOUD) changed following Medicaid’s pandemic-era enrollment freeze unwinding. In this cross-sectional study of 2.4 million US adults who filled buprenorphine prescriptions, the early unwinding period was associated with declines in the level and trend in patients receiving buprenorphine fills, driven by Medicaid-paid prescriptions, partially offset by increased commercial insurance and self-pay fills. States with higher automated (ex parte) Medicaid renewal rates and more income verification sources for automated renewals showed greater stability in buprenorphine access, highlighting the role of state policies.