Windows 11 build 21380

Windows 11 build 21380 is an early unconfirmed build of Windows 11 which was shown running on an Acer machine during the 2021 Hong Kong Computer and Communications Festival. A number of photographs detailing various aspects of the user interface as well as version information were posted on BetaArchive by member DiaoSlime in 21 August 2021. It is currently the earliest known build with available pictures.

The posted screenshots show the new Start menu and taskbar, which appear identical to the ones found in build 21996 and later. The watermark also includes the same notice that warns users not to take screenshots of the build, as seen in build 21990. The original poster stated that the user interface in general is very close to other available builds.

This build is one out of two known builds to be compiled from a branch with the  prefix, the other being Windows 10 build 21327 (fs_prerelease). The meaning of the prefix is currently unknown.