Windows Insiders are having a pretty busy day. Microsoft released Windows 10 build 17763 to the Fast ring, and there's a new cumulative update to test servicing in the Slow ring. The firm also released new ISOs for build 17758, and now there's a new SDK Preview, which is build 17758.
As you'd expect, there are no new features in today's SDK. In fact, we should be getting the final SDK for the Windows 10 October 2018 Update any day now. After all, Insiders will be getting the RTM build soon, if they don't have it already, and the update will be ready to ship.
Unlike some previous SDKs, this one will install on all supported versions of Windows 10. It can run side-by-side with other SDKs, so you can run it in a production environment as long as you don't target version 1809.
MSIX support is new in version 1809, but it's still not supported by the Microsoft Store or the App Certification Kit, although that will likely change once Microsoft starts accepting apps for Windows 10 version 1809 to the Store.
If you want to download the new SDK Preview, you can find it here.