Windows Longhorn build 4000
| Build of Windows Longhorn | |
 | |
| OS family | Windows NT |
|---|---|
| Version number | 6.0 |
| Build number | 4000 |
| Architecture | x86 |
| Compiled on | 2002 |
Windows Longhorn build 4000 is the first currently known Milestone 4 build of Windows Longhorn, which is mentioned in the setup of builds 4005 up until 4033, where it states that a user cannot perform an upgrade installation on a build lower than this build.