14.0 right now is still very similar to 13.0.
The whole scheme is pretty simple: There's one main development branch where all new work is done, this always has a version number XX.0-CURRENT.
For a major release, a "stable" branch is created, for example stable/13
and from that branch, all minor releases are branched off (we now have releng/13.0
for the first minor release of 13, 13.0-RELEASE).
Now, the "trick": As soon as a new "stable" branch is created, the version number in the main branch is incremented. Some time ago, we had 13.0-CURRENT, then, a stable branch for 13 was created (and also a release branch for 13.0, from which all the BETA and RC versions were built so far) – and at the same time, the version number in the main branch was set to 14, so it is 14.0-CURRENT now.
In a nutshell, this just means that the next major release branched off will be 14 – and when that happens, the main branch will instantly switch to 15.0-CURRENT.