This bill aims to significantly enhance federal support for behavioral health services under Medicaid by amending Title XIX of the Social Security Act. It provides a higher Federal matching rate for states' increased expenditures on these crucial services, which encompass mental health and substance use care. Specifically, the federal government will match 90% of the amount by which a state's current spending on behavioral health services exceeds its spending during the 4-quarter period ending March 31, 2019. To receive this increased federal funding, states must adhere to strict accountability and maintenance of effort requirements. States are mandated to use these funds to supplement, not supplant , their existing state expenditures for behavioral health services, ensuring new federal money expands access rather than replacing state contributions. Furthermore, the funds must be directed towards activities that improve the capacity, efficiency, and quality of behavioral health service delivery, including measures like increasing provider payment rates and reducing staff turnover. The Secretary of Health and Human Services is also required to issue guidance defining behavioral health services and submit annual reports to Congress on their provision, payment rates, and utilization under Medicaid.