A new Windows 10 SDK Insider Preview is available today in build 17125. Microsoft hasn't yet published a blog post to say what's new, but it's safe to assume that there are no new front-facing features. Now that we're so close to RTM for the spring update, it should be focusing on fixes and improvements.
The main variable will be whether or not it will install on non-Insider PCs. There's a known issue that's come and gone in various SDK builds where it can't be installed on machines that aren't running an Insider Preview version of Windows 10. Other than that, you can run it side-by-side with older SDKs, meaning that you can use SDK Preview build 17125 in a production environment as long as you target an older version of Windows 10.
Build 17125 coincides with the latest Slow ring and Fast ring builds, which are 17127 and 17133, respectively. If you want to test out your apps that are targeted at the latest build, you'll need to be on one of those. The SDK is also only formally supported on Visual Studio 2017.
Microsoft will likely publish a blog post about Windows 10 SDK Preview build 17125 today, and we'll keep you updated if there's anything new. To download the SDK, you can find it here.