Folks who make it a habit to browse through the AOSP source code have noticed some new numbers
A new branch of the code, jb-mr2.0.0-release, has been created in AOSP, and there are a couple new tags (android-4.3_r2.3 and android-4.3_r3.1) to go along with it.
This isn't really anything we shouldn't expect. Code as complicated as Jelly Bean is one of those things that is never finished, and the people writing it are always fiddling with new ideas and methods, and are prone to come back with new tweaks. When enough of those tweaks are committed, adding a new tag or branch becomes necessary. That's what tags and branches are for, after all.
You see, the source code for a project as big as Android needs special tools and special people to keep it in order. Tools like SVN or Git help the people working with code — both "officially" and as a hobby — keep track of which builds are current, and which builds are for which devices. That's done with — you guessed it — branches and tags. It's a great way to check out a code library and keep it current.
As for what these new branches and tags mean, well we're not going to speculate too much here. Usually a new branch means a new release at some point, but of course that new branch needs populated with changes worth updating first. In any case, Android software engineer Conley Owens says we'll see "an announcement email sent out about these by the end of this week." We'll keep an eye out for it.
Source: Android Building Google Group