Major changes are coming in the next WeeChat version, bumped to 4.0.0 (instead of 3.9, as planned initially).

Some breaking changes:

1. key bindings improvements: using names instead of raw codes (eg: meta-left instead of meta2-1;3D)
2. many identifiers have been made case sensitive, including commands, aliases and options
3. build with autotools has been removed, only CMake can now be used to compile WeeChat.

There are other changes, see the ChangeLog.
Note that this version is under development and your feedback is welcome!
Please read carefully the release notes if you're testing it: Release Notes.

Cherry on the cake: WeeChat is now following a "practical" semantic versioning, a less strict version of https://semver.org/.

For more information on all major/breaking changes, see the specifications: https://specs.weechat.org/