Microsoft has just announced that Windows 8.1 will launch on October 18 at 12:00am in New Zealand, which in Singapore time is October 17, 7:00pm. For existing Windows 8 users, the Windows 8.1 update is free, and will be available through the Windows Store. Windows 8.1 will also be available at retail and on new devices starting from October 18.
Windows 8.1 aims to advance the Windows 8 vision, and brings support to devices sporting 7 to 10-inch screen sizes; along with smarter search, richer multi-tasking, and a more powerful and harmonious Start screen that sees the return of the Start button (though not the Start menu). The final bits of Windows 8.1 is expected by the end of this month; known as Release to Manufacturing (RTM), it will first reach the hands of PC OEMs, so that new devices loaded with Windows 8.1 can be ready by October 18. According to The Verge, Microsoft is expected to continue working on Windows 8.1 between RTM and general availability.
Source: Windows Blog.