A new Windows 10 Creators update SDK is now available to download for developers and enthusiasts who want to explore. Interesting thing about this SDK is its Build version number 10.0.15063.400 which is newer than last released Creators update build.
Microsoft last pushed Windows 10 Build 15063.332 to non-insiders running Creators update. So, this SDK Build 10.0.15063.400 is higher or newer in Build creation hierarchy. It may pack extra fixes and improvements over the last released build for non-insiders.
The Windows 10 SDK (10.0.15063.400) provides the latest headers, libraries, metadata, and tools for building Windows 10 apps. The Windows 10 SDK, when used in conjunction with Visual Studio 2017, will provide the optimum experience for building apps for Windows- allowing you to take advantage of the latest tools and APIs delivered the Windows 10 Creators Update.