https://wccftech.com/first-windows-10-2021-build-is-out-with-new-wsl-features/

Microsoft has started to release fresh builds from 2021 Windows 10 feature updates. Today's is the first build going live for the newly minted Dev Channel (previously known as the Fast ring). This is the first build coming from the RS_PRERELEASE branch, which tests features for the upcoming versions of operating system.

Microsoft has already started testing Windows 10 20H2 through the Beta Channel (or the Slow ring), so features being tested through these builds will become part of Windows 10 2021 or later versions. As a reminder, Dev Channel builds aren't tied to specific versions of the operating system. The Windows maker said that the matchup will happen when the builds move to the Beta Channel. However, it is highly likely these new features will become part of either Windows 10 21H1 or 21H2.