At BUILD 2013 last week, Microsoft released the Windows 8.1 Preview, Visual Studio 2013 Preview, and the Windows SDK for Windows 8.1 Preview (included in the VS 2013 Preview). Note that RTM was released on October 17th, 2013.

As with the Windows 8.0 SDK, the Windows 8.1 SDK is where you’ll find Direct3D 11.2, Direct2D 1.2, DXGI 1.3, DirectXMath 3.05, a new HLSL complier (#47), and some updates to WIC. We recommend using the Windows 8.x SDK instead of the DirectX SDK, or at a minimum using the Windows 8.x SDK primarily with only specific usages of the legacy DirectX SDK.

The 18.0 C++ compiler in the Visual Studio 2013 Preview includes support for a new __vectorcall x86 and x64 calling-convention, and DirectXMath 3.05 has been updated to take advantage of it. I refreshed the DirectXMath extensions series, XDSP, and SHmath to integrate smoothly with this new version. The 18.0 C++ compiler supports additional C++11, Standard Library/STL, and C99 library features as well. See the Visual C++ Team blog, Somasegar’s blog, and the Visual Studio blog. Remote Debugging Tools packages are also available.

You’ll find VS 2013 projects for DirectXTex, DirectXTK, and Effects 11 on their respective Codeplex sites. There is a Windows Store app for Windows 8.1 version of DirectXTK Simple Sample available on MSDN Code Gallery.

The DirectX SDK (June 2010) is still available as the last release of the standalone DirectX SDK, but we strongly encourage developers to begin to transition to using the Windows SDK instead. Instructions for 'mixing' use of the new Windows SDK and older DirectX SDK content can be found here. Remember that for Windows Store app development, do not use the DirectX SDK.

VS 2010 Users: The standalone Windows 8.1 SDK does not integrate a new "platform toolset" option for Visual Studio 2010 to use the newer headers. See this post for more details.

Game Compatibility: For developers and publishers of Windows Desktop PC games, be sure to review the Desktop Games on Windows 8.x recommendations, the latest Windows and Windows Server compatibility cookbook, and pay particular attention to the new appcompat behavior of the GetVersion(Ex) API—which you aren’t using, right?

The key takeaway is if your game or launcher uses this API to collect user telemetry, be sure to add the compatibility manifest elements to your EXEs. Otherwise, get rid of any crusty OS version checks that still use this API.

Direct3D 11.2: Note that there is no D3D_FEATURE_LEVEL_11_2 hardware feature level defined as of yet. New hardware features exposed by DirectX 11.2 are optional.

Windows Family Safety / Parental Controls: Windows 8.1 supports the Russian Age Rating System--see the Windows 8.x and GDFs post as well as the updated GDFTrace utility. If you run GDFMaker from the Windows 8.x SDK on Windows 8.1, you'll have the option of populating the new rating system. Note support for RARS is added to Windows 8.0 via KB 2838466.

_WIN32_WINNT: When building an application that is 'down-level' using headers in the Windows 8.1 SDK, be sure to explicitly select the correct 'minimum' _WIN32_WINNT value. VS 2013 Preview and the Windows 8.1 SDK default to 0x0603. For Windows 8 compatibility, use 0x0602; for Windows 7 use 0x0601; and for Windows Vista use 0x0600. Typically this is done as part of the project configuration via Preprocessor Definitions. See Using the Windows Headers for more information.

Developer Runtime: The Windows 8.1 SDK (also included with Visual Studio 2013) is where you obtain the latest Developer Runtime that is compatible with Windows 8.1.

Windows Store app developers: Be sure to review the Migration Guide and how to Retarget to Windows 8.1 Preview.

System requirements: Windows 8.1 will run on the majority of hardware that can run Windows 8. The 64-bit version does require CPU support for some additional instructions which are not present on early first-generation 64-bit processors. See the Windows 8.1 Preview FAQ for details.

Visual Studio 2013 can be installed on Windows 8.1, Windows 8, and Windows 7 Service Pack 1. For Windows 7 SP1, installing KB 2670838 is required as part of the setup.

DirectX SDK: If you want to make use of legacy DirectX SDK components such as D3DX9, D3DX10, D3DX11, or XAudio 2.7 with Visual Studio 2013, see MSDN for details on mixing the paths correctly.

D3DX: As noted on MDSN, all versions of D3DX are deprecated including D3DX11. See Living without D3DX.

Related: Where is the DirectX SDK?, DirectX SDKs of a certain age, Visual Studio 2013 Release Candidate, Visual Studio 2013 and Windows 8.1 SDK RTM are now available

See also: Where is DXERR.LIB?,  BC6H/BC7Encoder, Effects for Direct3D 11 Update, DXUT for Win32 Desktop Update, DirectX SDK Samples Catalog