Microsoft just announced on Windows blog about the release of RTM (Release To Manufacturing) of Windows 8.1, Windows 8.1 Pro and Windows Server 2012 R2 for MSDN and TechNet Subscribers. Windows 8.1 Enterprise edition RTM is not yet released. It will be made available on MSDN and TechNet later this month.
Microsoft stated that the developer partners and IT pros were waiting eagerly for Windows 8.1 RTM so that they can move forward in app development & deployment tasks. So on the basis of feedback from them Microsoft finally made available RTM bits for developers and IT professionals. Now one can easily build or test Windows 8.1 apps on the RTM of Windows 8.1. Windows 8.1 RTM is having build number 9600.
This release is not for the store and end-users have to wait for October 18th for the general availability of Windows 8.1. Along with this Microsoft also released the Visual Studio 2013 Release Candidate which can be downloaded now.