Medicaid Coverage for Addiction Recovery Expansion Act This bill amends title XIX (Medicaid) of the Social Security Act to allow states to provide medical assistance to adults for residential addiction treatment facility services under the Medicaid program if such services are offered as part of a full continuum of evidence-based treatment services. "Residential addiction treatment facility services" are medically necessary inpatient services provided in an accredited, size-limited facility for the purpose of treating a substance use disorder within a specified time period. The provision of medical assistance for such services to an individual shall not prohibit federal financial participation for medical assistance with respect to other services provided to the individual within the same time period. Subject to specified conditions, a woman who is eligible for medical assistance on the basis of being pregnant may remain eligible for residential addiction treatment facility services for specified time periods without regard to eligibility limits that would otherwise apply as a result of her pregnancy ending. In addition, the bill establishes a grant program for states to expand infrastructure and treatment capabilities of existing youth addiction treatment facilities that: (1) provide addiction treatment services to youths under Medicaid or the Children's Health Insurance Program (CHIP), and (2) are located in communities with high numbers of medically underserved populations of at-risk youths. At least 15% of grant funds awarded to a state must be used for making payments to rural facilities.