According to the latest reports, Windows 8.1 will be available to all users in mid-October, roughly one year after Microsoft launched Windows 8 to the public. Microsoft is expected to deliver RTM Windows 8.1 code to OEMs by the end of August, although unlike previous years the RTM release won't be available on MSDN or TechNet at that time; instead Microsoft will be holding back the launch until October for all channels.
Along with general availability of the refreshed OS, new hardware running Windows 8.1 is expected to launch alongside it, according to Mary Jo Foley of ZDNet. October is the perfect time for new devices to be released, as it's the lead-up to the holiday season, and if the date holds true, Microsoft would have delivered on their promise to refresh Windows in under 12 months.
Holding back the release of Windows 8.1 by two full months from the date it is technically finished might prove beneficial to Microsoft. They would be able to fix any zero-day bugs, as they are discovered by OEMs before the general release, as well as building up some hype ahead of launch. When Windows 8 was released, many people had already installed the operating system through various channels such as MSDN, and most of the features were already revealed (and criticized), making the launch fairly unexciting.
Windows 8.1 will be a free update for all current Windows 8 users, bringing a range of usability enhancements and fixes, supposedly taking care of some of issues people had with Windows 8, as well as bringing new features and functionality. The Start button is set to make a partial return (just a button, not the menu), as will an option to boot straight to the desktop, Start screen improvements such as new tile sizes and more customization. A pre-release build of Windows 8.1 (9471) leaked recently showing that the OS will also bring more detailed tutorials for users struggling to adapt to the changes in the OS.