A new Avo version is released every two weeks, usually on Tuesday. The versioning scheme does not follow semver but a series release.
The current series is series 2 (version 2.1, 2.2, 2.9, etc). Every two weeks we'll increment the minor version number (from 2.7 to 2.8).
In-between that release cycle we might release patches (2.7.1 or 2.9.5) that address particular bugs or issues that are more urgent and can't wait for the next release cycle.
Sometimes I publish pre-releases (2.7.1.pre.1 or 2.5.2.pre.7).
The pre-releases are usually built on my machine and will be builds from a specific branch, so they don't follow any particular convention. The pre.2 might contain a fix, but the pre.3 might not containt tht fix because they might be built from different branches. I usually mention on a PR or issue to the bug reporter if they should or shouldn't use pre-releases. They won't get installed in regular bundle update avo commands, unless you instruct it in the Gemfile.