Microsoft is still not “done” with Windows 10 “Redstone 4” — the next release of Windows likely to be named Spring Creators Update/1803.

On March 13, Microsoft rolled out to Insider testers in the Fast Ring Build 17120. This build includes a few tweaks to Windows Defender ATP, specifically for Windows Defender Application Guard (WDAG) and Windows Defender System Guard.

Windows Defender Advanced Threat Protection (ATP) is a suite of tools that includes Defender Application Guard, Device Guard and Antivirus.

Build 17120 includes performance improvements to WDAG so that the start up process is lighter and faster. It also adds the option to download files from within WDAG to the host (in the Enterprise edition). With Windows Defender System Guard, Microsoft is adding a new level of security by adding Memory integrity (hypervisor-protected code integrity) in Core Isolation as part of its work around virtualization-based security.

Microsoft still has several known issues in the Mixed Reality features that are coming with Redstone 4 around performance, inbox apps failing to load, crashes when launching the Store from Movies & TV, sound and video rendering. These are itemized in today’s blog post.

Microsoft also released an ISO of last week’s Redstone 4 test build (17115) today. (So far, only the 32-bit version is showing up for some.)

Microsoft also is making available today Project Honolulu Technical Preview 1803 and a Remote Server Administration Tools (RSAT) preview that can be installed on Windows 10 Insider build 17110 or higher. Honolulu is a graphical management tool for Windows Server. The Honolulu preview fixes lots of bugs and also adds Azure Active Directory (AAD)-based access control, plus a couple of other more minor features. The RSAT preview includes a couple of fixes.

Microsoft is due to finalize Redstone 4 some time this month (March) and will start to roll out the release the following month, as it has done with the last few Windows 10 test builds.