Windows 8.1 build 9600 (fbl uex drx)

This build was confirmed by a Channel 9 video Smart Files in SkyDrive and Windows 8.1.

It's the first confirmed build after the RTM, which had the same build number but an earlier date. The lab name comes from The Windows Live DRX team (Windows Live Devices & Roaming Experience), which produces the SkyDrive client applications.

Given its short period after RTM's compile date, it probably doesn't contain many changes. The desktop contains a "SkyDrive sync diag..." ...nostics?, which may mean that it has some internal features, just for debugging SkyDrive.