Microsoft has been testing some of the early builds of Windows 10 Redstone 4 with Windows Insiders over the past month or so. The company kicked off Redstone 4 with Insiders part of Skip Ahead at first, but later expanded the availability to include all Windows Insiders after the release of the Fall Creators Update.
Today, it is releasing the ISOs for Windows 10 Redstone 4 Build 17025, and you can use the ISOs to perform a clean install or checkout the progress with Redstone 4 on a virtual machine instead. There aren’t a lot of new features in the early Redstone 4 builds, but Microsoft has been making some minor changes and improvements to the OS and added some new Fluent Design changes to the OS as well.
You can get the ISOs for build 17025, as well as the additional downloads from the Windows Insider site here.