Windows Longhorn build 4000

Windows Longhorn build 4000 is mentioned in the setup of Longhorn builds up to and including build 4033, where it states that a user cannot perform an upgrade installation on a build lower than 4000. On 2020-02-22, a YouTube user claimed to have this build in his unleaked build 5002 video, and claimed it uses the WinPE installation method like 4001.