---
title: 'FHIR Implementation Guide'
description: 'The Huli FHIR Implementation Guide — canonical profiles, extensions, and value sets for FHIR R4 and R5.'
nav: 'API / FHIR IG'
order: 2
version: v1
source: generated
updated: '2026-09-23'
---

# 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/](https://developers.huli.ai/fhir/r4/) — the stable default.
- **FHIR R5** — [developers.huli.ai/fhir/r5](https://developers.huli.ai/fhir/r5) — publishing soon.

<Callout variant="note">
The R5 Implementation Guide is still being deployed; its link goes live when R5 ships. R4 is the stable default today.
</Callout>

For a resource-by-resource overview inside these docs, see [FHIR resources](/v1/api/resources).