Windows Neptune build 5111

Windows Neptune build 5.50.5111 is a beta build of Windows Neptune. As of 2017, it is the only known leaked build of Windows Neptune. It is also known as Microsoft Neptune Developer Release, however much of the branding (including in winver) is still that of Windows 2000. The reported build string is "5.00.5111". This build cannot be upgraded from an earlier build, just be installed as a clean install.

It was compiled on 1999-12-10. It was sent to developers on the 27th. Other builds may have existed, most confirmations of other builds existing come from various files in Windows Millennium builds holding a Neptune version number.

It introduces Activity Center, a new login interface, and changes to Help and Support and certain Control Panel programs. It will also hibernate by default.