FHIR Implementation Guide

The Huli FHIR Implementation Guide (IG) is the canonical set of profiles, extensions, and value sets the API validates against — one guide per release. It documents the exact resource shapes, cardinalities, and terminology bindings your integration must conform to.

• FHIR R4 — developers.huli.ai/fhir/r4/ — the stable default.
• FHIR R5 — developers.huli.ai/fhir/r5 — publishing soon.

For a resource-by-resource overview inside these docs, see FHIR resources.