This bill permanently allows state Medicaid programs to receive federal payment for substance-use disorder services that are provided at institutions for mental diseases (IMDs) for individuals aged 21 to 64. The bill also extends the maximum length of stay over a 12-month period from 30 days to 45 days. In addition, the bill provides statutory authority for a 2018 letter from the Centers for Medicare & Medicaid Services that provided for Medicaid demonstration programs for IMD mental health services for adults and children; the bill similarly increases the average length of stay under such programs to 45 days.