42 C.F.R. § 435.150
(b) Eligibility. The agency must provide Medicaid to individuals who:
(3) Were in foster care under the responsibility of the State or a Tribe within the State and enrolled in Medicaid under the State's Medicaid State plan or under a section 1115 demonstration project upon attaining:
(c) Options. At the State option, the agency may provide Medicaid to individuals who meet the requirements at paragraphs (b)(1) and (2) of this section, were in foster care under the responsibility of the State or Tribe within the State upon attaining either age described in paragraph (b)(3)(i) or (ii) of this section, and were:
(2) Placed by the State or Tribe in another State and, while in such placement, were enrolled in the other State's Medicaid State plan or under a section 1115 demonstration project:
[81 FR 86451, Nov. 30, 2016]