Windows 11 build 21327

Windows 11 build 21327 is the earliest known build of Windows 11. It was mentioned in an issue posted to Visual Studio's Developer Community by a Microsoft employee on 11 March 2021. As the build tag is repeated there multiple times throughout the thread, it is unlikely that it is a typo of 21327.1000.rs_prerelease.210226-1437.

This build is one out of two known builds to be compiled from a branch with the  prefix, the other being Windows 11 build 21380. The prefix stands for Fire Steel, the codename for an internal Microsoft tool related to Windows 11 development.