Most time, I think json is forward and backward compatible as long as some convention is kept such as adding fields only etc. I always thought so since I studied CQRS and event sourcing. Is it true for FHIR, especially firely sdk? I answered so in a discussion, however I doubted it as I didn’t do it in FHIR. Here I have a short code to demostrate the two case. In the end, the result is yes and no.