Microsoft has released the Windows 10 PC build 10586.338 for Insiders who are signed up to get Release Preview versions.

Windows 10

As WSPU notes, this build is a preview of the next cumulative update for Windows 10 version 1511, which is likely just for bug fixes and minor improvements. This Release Preview version for Insiders is just to stamp out some remaining bugs before it is released to all Windows 10 users. That release could happen as early as next week.