Windows Longhorn build 3663

Windows "Longhorn" build 3663 is the earliest known build of Windows Longhorn for which screenshots exist, and possibly the first build based on the Windows Server 2003 Release Candidate 1 codebase. As of 2021, this build remains unleaked. A rumor exists that the build was leaked in the far past, but due to the low interest, the download links were permanently removed. There is no evidence to support this rumor, however, and it can be safely assumed that there was never any leak beyond a few screenshots. However, there is uncertainty over whether some of the screenshots are genuine, as one of the system properties screenshots features inconsistent use of fonts.

Visual changes in the build include replacement of the colored Windows flag on the start button with a single white color variant. It also seems to have the login screen from build 3683 and disk space indicators in Explorer in screenshots that are not taken by Calvin Zhang. Otherwise, this build is not much different from Windows XP or Server 2003.