HAPI-FHIR uses Semantic Versioning.
Versioning System 6.3.x+
Starting November 2022 (HAPI-FHIR 6.3) HAPI-FHIR adopted a new version numbering system.
Official Release
<MAJOR>.<MINOR>.<PATCH> where MINOR is an even number.
E.g. 6.4.12
Snapshot Release
<MAJOR>.<MINOR>.<PATCH>-SNAPSHOT where MINOR is an odd number.
e.g. 6.3.27-SNAPSHOT
Versioning System 1.0.0 - 6.2.x
Prior to 6.3 (Nov 2022), HAPI-FHIR used the following version numbering system:
Official Release
<MAJOR>.<MINOR>.<PATCH>
e.g. 6.1.2
Snapshot Release
<MAJOR>.<MINOR>.0-PRE<PATCH>-SNAPSHOT where <MAJOR>.<MINOR> is the version number of the next release.
e.g. 6.1.0-PRE27-SNAPSHOT