Windows 8.1
From BetaArchive Wiki
Windows Blue is the rumoured up-coming operating system by Microsoft to succeed Windows 8. With Windows 8, Microsoft changed the release cycle of Windows (similar to the one Apple uses), so "Codename Blue" is supposedly already in development.
Rumours found online indicate Windows Blue is to be a minor update to Windows 8 (possibly offered as a free upgrade). The relation between Windows Blue and Windows 9 is known, but it is possible that 9 will follow Blue as a major update.
Builds
Windows "Blue" build 9220 - it is unclear whether this is Windows 8 post-RTM build or a very early build of Blue
[Windows "Blue" build 9364] - First leaked build, M1?
