Update (August 27, 2013): Microsoft has announced that Windows 8.1 and Windows RT 8.1 have been released to manufacturing. In the past, when this milestone was reached, we would wonder when the OS would be available to the public. However, there's no need to speculate this time round, as Microsoft has already said that it'll arrive on October 17 (that's Singapore time) on the Windows Store for existing Windows 8 and RT users. Retail copies and new devices loaded with the new OS are expected to hit a day later, on October 18.
Originally posted on July 9, 2013:
Microsoft’s chief marketing officer for Windows, Tami Reller, has announced at the company’s Worldwide Partner Conference that Windows 8.1 - the first major update to Windows 8 - will RTM (release to manufacturing) at the end of August. This means that new PCs and tablets sporting Windows 8.1 are likely to arrive as early as September.
While there’s no word on when current Windows 8 users will be able to upgrade to Windows 8.1, we see no reason why it won’t be delivered at the same time as RTM, or shortly after. The update will be deployed via the Windows Store, and is free to all Windows 8 and Windows RT users.
For those interested to test out the updated OS, Microsoft has since June 26 released a public preview of Windows 8.1. Besides bringing back the Start button (though not the Start menu), Windows 8.1 is stuffed with tweaks, fixes, and new features, such as a revamped Windows Store, further touch optimizations in Internet Explorer 11, system-integrated Bing search, a re-written PC settings interface, and vastly updated built-in apps.