The release notes for this version of the Second LifeTM Viewer were published August 12th. There are about 33 fixes and additions. There are eight known issues that remain. Your viewer will automatically update to this version if you are using the default setting to automatically update.
If you have “Willing to update to release candidates” enabled, you may get a release candidate. I’m still flipping coins on whether that is a good idea or not. I’ve mostly decided I need to turn off Automatic updates for everything except the main SL Viewer and I have ‘Willing’ disabled on all my viewers. I do install release candidates, but manually.
This version of the SL Viewer Second Life 3.6.3-279564 was put into RC status Aug 6, 2013. Just yesterday it was promoted to the main release. This is the exact same viewer that was the RC, which is the point.