Sources close to cnBeta have confirmed that the Windows 8.1 RTM version number 6.3.9600. Typically the final build number, from Vista on up, has been evenly divisible by 16 and is artificially bumped up to ensure this happens. You may recall that the Windows 8.0 RTM build number was 9200. Windows 95?s build number was 950, Windows 98?s build number was 1998, Windows 98 SE was 2222, and Windows XP was 2600 (reference to hacker magazine), Windows Vista 6000 and Windows 7 was 7600.
Screenshots of build 9484, recently released to OEMs, have recently leaked and build 9477 leaked to the web a few days back. Microsoft-news can confirm Microsoft is now working on the RTM branch of Windows 8.1, no new features are being added, only critical bugs are being fixed, especially those that are high priority for OEMs. As previously reported Windows 8.1 will be released around October 18th.