This bill seeks to amend Title XIX of the Social Security Act to allow for Federal financial participation (FFP) under the Medicaid program for services provided to patients in an institution for mental diseases (IMD). Currently, federal law generally prohibits Medicaid from covering care in IMDs for adults, limiting states' ability to fund inpatient mental health treatment. The legislation specifically removes several clauses in Section 1905(a) that exclude services in an IMD from Medicaid's definition of covered medical assistance. By eliminating these exclusions, the bill would enable states to receive federal matching funds for a broader range of inpatient mental health services. These amendments are designated to apply to medical assistance furnished on or after January 1, 2027, thereby expanding Medicaid coverage for mental health care.