Windows 10 build 21381.1000

Windows 10 build 21381 (co_release_prs) is a build of Cobalt, the 21H2 development semester of Windows as a service. It was mentioned in the file  in the Windows Driver Kit for Windows 11 build 22000.1.

vsixversion.txt
\\winbuilds\release\CO_RELEASE_PRS\21381.1000.210510-1427