Windows Neptune build 5111

Windows Neptune build 5.50.5111 is a beta build of Windows Neptune. As of January 2018, 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 sent to developers on 1999-12-27. 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.

Most builds released online has been modified to not require a product key, has no timebomb, and replaces mentions of "Windows 2000" during the setup to "Neptune". However, some builds like the one on BetaArchive does not modify the Windows 2000 strings and has the timebomb and product key.