Microsoft today released Windows Server Insider Preview build 18945, aligning the build number with the one for Windows 10 released last week and also the Windows 10 SDK, which was released today as well. Unlike the SDK, there doesn't seem to be a whole lot that's new with this release though.
The single feature noted in the blog post is support for FIDO2 security keys in hybrid environments. Earlier this month, Microsoft announced support for this authentication method in cloud environments with Azure AD, but this update extends the capability to allow security keys to be used for Single Sign-ON (SSO) in on-premises environments.
The new build can be downloaded from the Windows Insider website, and it comes with the usual complementary downloads, including language packs and the Core App Compatibility Feature-on-Demand (FoD). Just as with the previous build, it won't expire until July 31 of next year, so that shouldn't be a problem.
Microsoft also recently released the preview version of Windows Admin Center 1907, which includes a few quality-of-life improvements. You can find it in the Windows Insider website as well.