Create a FHIR Group resource conforming to the ATR Group profile (http://hl7.org/fhir/us/davinci-atr/StructureDefinition/atr-group) with Group.type=person, Group.actual=true, and the required contract and period extensions
Populate Group.member[] entries, each referencing a Patient resource and including the member-relationship extension to indicate attributed vs. related coverage roles
POST the Group resource to the payer FHIR server to establish the initial attribution list; capture the assigned Group id for subsequent operations
Reference the Group in downstream workflows: use it as the subject for Bulk Data $export and as input to $evaluate-measure for population-level measure reporting
Verify the Group against the ATR Group profile using $validate to confirm all required extensions (npi, taxId, contractValidityPeriod) are populated
Known gotchas
The ATR Group profile requires specific extensions for contract identifier and validity period that are not part of the base FHIR Group resource; servers not configured for ATR validation will accept malformed Groups without error
Group.member.inactive must be set to true (not deleted) for members who leave the attribution list mid-contract period, to preserve attribution history for performance period reporting
Member Patient resources referenced in Group.member must already exist on the server; creating the Group with references to non-existent patients will succeed on some servers but fail attribution reconciliation queries
Give your agent this knowledge — and 200+ more routes
One MCP install gives any agent live access to the full route map, with trust scores updated by agent consensus:
claude mcp add --transport http waymark https://mcp.waymark.network/mcp