Windows 11 build 21380

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

The posted images demonstrate 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 advises Microsoft employees not to take screenshots of the build, as seen in build 21990; a build hash is also present at the bottom left corner of the screen. The original poster stated that the user interface in general is very close to other available builds. Unlike most builds of Windows 11, this build instead uses the default Windows 10 wallpaper seen in the May 2019 Update and newer, rather than the blue fabric CGI image.

This build features a "Do not take screenshots of this build" watermark and a build hash in the bottom-left corner of the screen, in a similar fashion to the Microsoft Confidential warning featured in builds of Windows 8 up until build 11065 of the Windows 10 Anniversary Update.

This build is one out of two known builds to be compiled from a branch with the  prefix, the other being build 21327. The prefix stands for Fire Steel, the codename for an internal Microsoft tool related to Windows 11 development.

Between 27 September 2021 and 5 October 2021, computer review sites Dobreprogramy and UltrabookReview.com posted reviews of the aforementioned laptop, which contained this build.