In the first paragraph, the IG states: "Health Plans SHALL map claims and clinical information for a member to US Core v3.1.1 FHIR Resources based on R4."

In the third paragraph, the URL behind "US Core FHIR R4" resolves to https://www.hl7.org/fhir/us/core/index.html, which is (v6.0.0: STU 6).

If we really do mean US Core v3.1.1, that URL should be http://hl7.org/fhir/us/core/STU3.1.1.