Microsoft announced yesterday that they will be making Windows 8.1 RTM / Windows Server 2012 RTM & Visual Studio 2013 RC made available for developer community based on feedback received. This was a slight deviation from previous communication when both products hit internal RTM milestone. however I’m extremely pleased for being able to obtain RTM bits for both Windows Client & Windows Server prior to GA milestone which is 18th October.
At this point in time current RTM release is only available for TECHNET / MSDN Subscribers. There will be an Enterprise Version of Windows 8.1 which will be made available later this month to Enterprise Customers via Volume Licensing Service Center.
more information relating to official statement from Microsoft regarding RTM release please refer
Visual Studio 2013 RC can be downloaded from link below
Previous announcement relating to RTM/GA for Windows Server / Windows Client