VS 2013 RC includes the Windows 8.1 SDK. As with VS 2012 / Windows 8.0 SDK, this release integrates many aspects of the legacy DirectX SDK. As discussed in Where is the DirectX SDK (2013 Edition)?, there's new support for Direct3D 11.2, Direct2D 1.2, DXGI 1.3, HLSL Compiler #47, updates to WIC, and many new 18.0 C++ compiler features (such as __vectorcall). The Windows 8.1 SDK included in VS 2013 RC also includes DirectXMath 3.06 with a few minor changes compared to 3.05 in the Preview (see MSDN and this post). For more information on VS 2013 RC, see the Visual C++ Team blog, Somasegar's blog, and the Visual Studio blog.
For a comparison summary of new C++11 language features in VS 2013, take a look at the tables in the Dual-use Coding Techniques for Games post which have been refreshed for the latest toolset.
Windows 8.1: In related news, the Windows 8.1 RTM is now available on MSDN/TechNet for subscribers, with GA set for October 18, 2013. If you are developing Win32 desktop games, be sure to review the official appcompat cookbook and this post.
For developers working on Windows Store apps, see New APIs and features for developers and the Migration Guide from Windows 8. If you do not have access to the Windows 8.1 RTM build via a MSDN or TechNet subscription, you should continue to use VS 2013 Preview to develop and test Windows Store apps for Windows 8.1 Preview until GA.