Cobalt

Cobalt is the 21H2 development semester of Windows as a service, the commercial release of which is Windows 11. Work on Cobalt began in October 2020, although it did not replace Iron in the Dev Channel until December. It was later followed by Nickel in the second half of 2021.

Wave 2 (Windows 11)
See Windows 11 (original release) § List of known builds.