Based on reports of the Alpha builds of Warlords of Draenor, this is the Alpha and Beta patch version. Traditionally in World of Warcraft development #.0.0 releases are alphas or do not exist, but the pattern seems to be changing with this expansion as 6.0.0 appears to be the systems patch and 6.0.1 the alpha and or expansion release. With build 18764, the patch version was changed to Patch 6.0.2, but the reason was not clear.