Today, Paul Thurrot has shared the following info via twitter:
Spoiler
Although it does not follow directly from his tweet, most of us know that MS releases its OS with similar 'round' build numbers. So, we can expect Windows 8.1 RTM in next few days. The full build string reads 9600.16384.winblue_rtm.130821-1623, this differs slightly from the recently rumored build number 9600.16384.winblue_rtm.130822-2140. Until we have an official announcement from Microsoft, or leaks from trusted sources, we can only speculate on what this build number actually means. We do know that 9600 is going to be the official RTM, but what we're waiting for is to see if Microsoft change the 5 digit number.
via Twitter: https://twitter.com/thurrott/status/370990945879478272