As of the release of version 4.0.2 in December 2000, XFree86 has three release branches. First is trunk of the CVS repository. This is the main development stream, where all new work and work for future releases is done.
Second is the stable bugfix branch for the latest full release
(4.2.1). It is created around the time of the release. The branch
for this one is called "xf-4_2-branch". Fixes for bugs found
in the release will be added to this branch (as well as the trunk), and
updates to this release (if any) will be cut from this branch. Similar
stable branches are present for previous full releases.
Finally there is the 3.3.x legacy branch, which is called
"xf-3_3-branch". While this branch is not actively being
maintained, it does include some important post-3.3.6 bug fixes and
security updates. Relevant security updates in particular are usually
back-ported to this branch.
XFree86 is planning to make full releases from the main development stream approximately every six months, in late May and November of each year. The feature freezes for these releases will be 1 April and 1 October respectively. These are target dates, not a binding commitment. How effectively these dates can be met will depend to a large degree on the resource available to XFree86. Full releases consist of full source code tarballs, plus full binary distributions for a range of supported platforms. Update/bugfix releases will be made on an as-required basis, depending also on the availability of resources. Update/bugfix releases will not be full releases, and will consist of source code patches, plus binary updates to be layered on top of the previous full release.
The next full release will be version 4.3.0, tentatively scheduled for late late 2002. There is no scheduled update release. If there is one, the version will be 4.2.2.
Aside from actual releases, snapshots of the active release branches are tagged in the CVS repository from time to time. Each such snapshot has an identifiable version number.