Microsoft has officially released Windows 8.1 RTM available for download via Technet and MSDN, however, users must have a valid subscription to either web site.
Microsoft has just released RTM (Release to Manufacturing) version of Windows 8.1 and Windows Server 2012 R2 for their MSDN and TechNet subscribers, while Windows 8.1 Enterprise version will be available later this month.
This is the same build 9600 which has already delivered to OEM partners in late August, even though Microsoft aims this release for testing purpose only. Microsoft is still continuing to refine and update prior to Windows 8.1 general availability.
The software maker often distributes the OS via MSDN and TechNet as soon as they finalizes the RTM build, but this time, Microsoft had no plans to follow traditions. In consequence, they were facing strong criticism from developer partners and IT professionals, but Microsoft had to listen the feedback and extended availability of Windows 8.1 RTM.
Alongside the early Windows 8.1 availability for paid-subscribers, Microsoft is also releasing the Visual Studio 2013 RC today, which is available publicly. The Redmond group has planned to release the final version of Visual Studio 2013 along with Windows 8.1 GA and developers may need to tweak their apps to validate workings on Windows 8.1.
The release candidate of Visual Studio 2013 does not support Windows 8.1 Preview or Windows Server 2012 R2 Preview, and require Windows 8.1 RTM only for Windows Store app development.
The final release of Windows 8.1 will be available in stores as of October 18, 2013.