While Microsoft continues to creep toward finalizing Windows 10 “Redstone 4” for PCs, the company this week delivered its first Redstone 4 test build for the HoloLens.

Microsoft hasn’t delivered a significant Windows 10 update specifically for the HoloLens since the Windows 10 Anniversary Update in 2016, according to Windows Central. Instead, Microsoft has been focusing on adding new Mixed Reality features to Windows 10 as part of the last few feature updates and has several new Mixed Reality features slated to be part of Redstone 4.

The first Redstone 4 test build for HoloLens is Build 17123, which is a few builds older than the latest version of Redstone 4 that Insiders are testing on PCs.

As noted in the HoloLens RS4 Preview documentation, dated March 23, on the Microsoft documentation site, this test build is available to all HoloLens users. However, installing the preview will result in the erasing of all users’ content and restore the device to factory settings.

To install the preview, users first need to grab the latest version of the Windows Device Recovery Tool, and to make sure their HoloLens goggles are enrolled in the Windows Insider Program.

The documentation lists the new features coming to HoloLens via Windows 10 Redstone 4. Among them:

• Auto-placement of 2D and 3D content on launch
• Fluid app manipulation
• 2D app horizontal resize with reflow
• Expanded voice command support
• Updated Holograms and Photos apps
• Improved Mixed Reality capture
• Improved audio immersion
• File Explorer support for moving and deleting files from within HoloLens
• Media Transfer Protocol support for allowing desktop PCs to access photos, videos and docs on HoloLens
• Ability to set up HoloLens on a guest network using captive portal

The test build also includes some features specific to developers around spatial mapping and app tailoring interfaces. It also has some features specific to commercial customers around multiple Azure Active Directory user support, mail sync and more; and some for IT pros around setup, diagnostics and more.

Windows 10 Redstone 4, likely to be called the Spring Creators Update, is scheduled to start rolling out in April. There’s no word on when the final version of Redstone 4 will go to HoloLens users not in the Insider program, but it should be around that same time.

Microsoft officials haven’t said when to expect a new HoloLens design to be available, but have said the next-generation HoloLens device will include an AI coprocessor. Last year, potential delivery dates of late 2018 or 2019 were floated by tipsters.