Each release of ViennaCL carries a three-fold version number:

 ViennaCL X.Y.Z

For users migrating from an older release of ViennaCL to a new one, the following guidelines apply:

X is the major version number, starting with 1. A change in the major version number is not necessarily API-compatible with any versions of ViennaCL carrying a different major version number. In particular, end users of ViennaCL have to expect considerable code changes when changing between different major versions of ViennaCL.
Y denotes the minor version number, restarting with zero whenever the major version number changes. The minor version number is incremented whenever significant functionality is added to ViennaCL. The API of an older release of ViennaCL with smaller minor version number (but same major version number) is essentially compatible to the new version. Users of ViennaCL usually do not have to alter their application code, unless they have used a certain functionality that was not intended to be used and removed in the new version.
Z is the revision number. If either the major or the minor version number changes, the revision number is reset to zero. Releases of ViennaCL, which only differ in their revision number, are API compatible. Typically, the revision number is increased whenever bugfixes are applied, compute kernels are improved or some extra, not significant functionality is added.

Always try to use the latest version of ViennaCL before submitting bug reports!