The most recent version of FHIR is R5, released in 2023.
If you go to the HL7 FHIR documentation, R5 is what you’ll see on the main pages. This does not mean you should be using it.
If you’re starting a new project that uses FHIR, one of the first questions you’ll ask yourself is which version to use.
Most people will immediately go with R5. Why wouldn’t they?
- It’s the latest version
- It has a “richer” and improved data model
- Many gaps or issues will have been dealt with
- No worries about upgrading later
- It’s front and center on the HL7 FHIR home page
But FHIR is not “just another API”.
The decision of which version to use is not a casual one and is not one that should be made by the technical team.
In some countries, regulations govern the use of FHIR. Some of these regulations mandate the use of specific versions: R4 in particular.
The US is one of these countries.
R4 was released in 2019 and is in widespread use by businesses and organizations around the world.
The chart below is drawn from a survey I ran of FHIR users last year. The figures align very well with the official HL7 2024 State of FHIR Survey.
Almost 83% of organizations that use FHIR are using R4.
Most of these organizations have no intention up upgrading to R5.
If you build a solution that relies on R5 you may run into real difficulties when you try to interact with data providers and consumers who expect R4. In certain countries you may fall foul of one regulation or another that prevents your app or solution being used in that country.
The message here is to be careful when deciding on a FHIR version. Don’t assume that latest is best, or at least best for you and for your product.
Here’s the documentation link for R4: https://hl7.org/fhir/R4/resourcelist.html
Always hard to find if you haven’t bookmarked it.
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