It's been a big day for Windows Insider news. There are new Windows 10 builds available in both the Fast ring and the Slow ring. But also, Microsoft released a new Windows 10 SDK Insider Preview, bringing the build number to 17754.
We're reaching the tail end of the Redstone 5 development cycle, and the Windows 10 October 2018 Update should be finalized this month. In fact, it's possible that Microsoft will announce the final SDK at its Ignite 2018 conference later this month. But because of this, there are no new features in today's build.
One thing that's different than previous SDKs, however, is that this can be installed on all supported versions of Windows 10, rather than just Insider Previews. It can run side-by-side with other SDKs, so you can use it in a production environment as long as your app doesn't target Windows 10 version 1809.
One of the major features coming in the SDK will be MSIX support, which isn't supported by the Microsoft Store or the App Certification Kit right now. That should change when Microsoft starts accepting app submissions for the Windows 10 October 2018 Update.
You can download the new SDK here.