Microsoft has released the Windows 10 Creators Update SDK. The SDK is now available for download and developers can get it right now and start building amazing apps that take advantage of new platform capabilities to deliver new experiences to users.
The new SDK for Creators Update contains numerous updates and improvements over the last Anniversary Update release. Developers can incorporate new visual effects, animations and transitions to give their app a unique feel. For apps using Windows Ink platform, certain improvements have been made to ink analysis and recognition, and an ink toolbar with new effects (tilt pencil) and tools (protractor for drawing curves and circles).
For an accessory like the Surface Dial, more powerful and flexible APIs for the Surface Dial. Also, significant Bluetooth improvements with Bluetooth LE GATT Server, and peripheral mode for easier discovery of Windows Devices.
You can find a more complete list here along with the latest developer documentation.