VersionNumberScheme

X.org inherited the XFree86 version numbering scheme:

The version numbering format is M.m.P.s, where M is the major version number, m is the minor version number, P is the patch level, and s is the snapshot number. Full releases have P set to zero, and it is incremented for each subsequent bug fix release on the post-release stable branch. The snapshot number s is present only for between-release snapshots of the development and stable branches.

Development Branch

Immediately after forming a release stable branch, the patch level number for the main development branch is bumped to 99, and the snapshot number is reset. The snapshot number is incremented for each tagged development snapshot. The GIT tag for snapshots is "xorg--M_m_P_s". When the development branch enters feature freeze, the snapshot number is bumped to 900, and a stable branch is created for the next full release. The branch is called "-M_m-branch". The snapshot number is incremented from there until the release is finalised. Each of these snapshots is a "release candidate". When the release is finalised, the minor version is incremented, the patch level is set to zero, and the snapshot number removed.

Here's an example which shows the version number sequence for the development leading up to version 4.1.0:

4.0.99.1

• The first snapshot of the pre-4.1 development branch.

4.0.99.23

• The twenty-third snapshot of the pre-4.1 development branch.

4.0.99.900

• The start of the 4.1 feature freeze, which marks the creation of the "xf-4_1-branch" branch. That branch is the "stable" branch for the 4.1.x releases.

4.0.99.903

• The third 4.1.0 release candidate.

4.1.0

• The 4.1.0 release.

4.1.99.1

• The first pre-4.2 development snapshot, which is the first main branch snapshot after creating the 4.1 stable branch.

Stable Branch

After a full release, the stable branch for the release will be maintained with bug fixes and important updates until the next full release. All snapshots on this branch are considered "release candidates", so the first is indicated by setting s to 901. The snapshot number is then incremented for each subsequent release candidate until the update release if finalised. The patch level value (P) is incremented for each update release.

Here's an example which shows the version number sequence for the 4.1.x stable branch.

4.0.99.900

• The start of the 4.1 feature freeze, which marks the creation of the "xf-4_1-branch" branch. That branch is the "stable" branch for the 4.1.x releases.

4.0.99.903

• The third 4.1.0 release candidate.

4.1.0

• The 4.1.0 release.

4.1.0.901

• The first pre 4.1.1 snapshot.

4.1.0.903

• The third pre 4.1.1 snapshot, also known as the third 4.1.1 release candidate.

4.1.1

• The 4.1.1 release.

4.1.1.901

• The first pre 4.1.2 snapshot.

4.1.2

• The 4.1.2 release.