@sivel wrote up ansible-core’s versioning scheme here: Ansible-core versioning
The ansible community package is using semantic versioning, since version 3.0.0, but ansible-core definitely does not (and never did, same as ansible before 3.0.0). Every 2.x.0 and 1.x.0 release had breaking changes, and these releases are called “major releases” in ansible-core’s versioning scheme.