Edit: more seriously it’s been since 3.0 after being on 2.6 forever
there are no special landmark features or incompatibilities related to the version number change, it’s simply a way to drop an inconvenient numbering system
It used to only get bumped after a major new feature update, but it was stable enough at 2.6 that it got stuck there for 8 years, so he switched to a different update number