Windows 8.1 RTM now avilable on MSDN and TechNet for download to developers

Windows 8.1 hands-on
Microsoft is reversing course today, allowing developers to download a final copy of Windows 8.1 ahead of its October 18th release. After originally announcing the finalization of the OS update last month, Microsoft was planning to hold back the final download for MSDN and TechNet subscribers until October 18th. The company now admits that was a mistake. "We heard from you that our decision to not initially release Windows 8.1 or Windows Server 2012 R2 RTM bits was a big challenge for our developer partners," says Microsoft. "We’ve listened and we get it."
Windows 8.1 Core and Pro editions will both be made available today on MSDN and TechNet, and the company is also launching a Release Candidate of Visual Studio 2013 for developers. Enterprise versions of Windows 8.1 are expected to be made available on the subscription services by the end of September. Despite the availability of the Release to Manufacturing (RTM) version of Windows 8.1, Microsoft is still stressing that this isn't really the final copy of the OS.
"We’re confident this pre-release will enable developers to make progress to ready their Windows 8.1 apps," says Microsoft, while noting that final refinement of apps will be needed at the October 18th release of the update. Sources familiar with Microsoft's plans have revealed toThe Verge that the company is still working on its built-in Windows 8.1 apps, and several bugs it wants to address before the October 18th release. Similarly, Microsoft is also planning to update Windows 8.1, and its built-in apps, regularly over the coming months. While in the past RTM has always signalled the finalization of a copy of Windows, Microsoft is seeking to redefine what's considered final and will continue to regularly update Windows 8 in the future
Source: The Verge