Windows Longhorn build 3663

Windows "Longhorn" build 3663 (with a build tag of 3663.Lab06_N.020728-1728) is the earliest known compilation of the Microsoft Windows "Longhorn" operating system for which screenshots exist, and possibly the first build based on the Windows Server 2003 Release Candidate 1 code base. The build has yet to leak to the general public.

This build technically introduced the Plex theme seen in later builds, but due to it being so early in development, the visual style was only a slightly updated version of the silver Luna theme introduced in Windows XP. The theme notably changes the four colors of the Windows flag on the Start button into a single white color. Otherwise, this build is not much different from previous versions of Windows XP.