During Microsoft's Worldwide Partner Conference earlier this year, the company revealed that Windows 8.1 would be made available to manufacturers by late August. According to recent reports, this has come true, with Microsoft's refreshed OS hitting the Release to Manufacturing (RTM) stage on August 23.
Both Mary Jo Foley and Paul Thurrott, veterans of Microsoft reporting, cited sources close to the company who confirmed that Windows 8.1 released to manufacturing on August 23, with a final build number of 9600.16384.130821-1623. It has been speculated that Microsoft didn't announce the RTM on Friday so that the news of CEO Steve Ballmer's retirement in the next 12 months wouldn't be overshadowed.
It's still expected that Microsoft won't release the Windows 8.1 RTM to TechNet or MSDN subscribers before its general release on October 18. This is relatively unusual for Microsoft, who in the past have released the RTM code to OEMs and IT professionals at the same time. Instead, it's expected that Microsoft will use the time between the RTM release and the general release to work on zero-day patches for any bugs discovered by OEMs.
For everyone currently running Windows 8, Microsoft will be delivering Windows 8.1 as a free update through the Windows Store. As previously reported, the update brings a number of new features and improvements over Windows 8. The Start button will partially return, search and multi-tasking have been greatly enhanced, the Start screen has been improved including new customization options, and the OS has been optimized for smaller tablets.