Release numbers consist of three parts, a major number, a minor number, and a revision number, each separated by a dot.

The major number is currently 1 (and has always been). It will only be bumped in case a new version offers a major change in the API that is not backwards compatible.

In the past (up to 1.6.x), even minor numbers have been used to indicate "stable" releases, and odd minor numbers have been reserved for development branches/versions. As the latter has never really been used, and maintaining a stable branch that eventually became effectively the same as the development version has proven to be just a cumbersome and tedious job, this scheme has given up in early 2010, so starting with 1.7.0, every minor number will be used. Minor numbers will be bumped upon judgement of the development team, whenever it seems appropriate, but at least in cases where some API was changed.

Starting with version 1.4.0, a file <avr/version.h> indicates the library version of an installed library tree.