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Unconfirmed build 
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Cobalt
| Version of Microsoft Windows | |
 | |
 | |
| OS family | Windows 11 (NT 10.0) |
|---|---|
| Semester | Cobalt |
| Architecture | x86,[a] x64, ARM64 |
| Replaces | |
| Iron | |
| Replaced by | |
| Nickel | |
Cobalt is the 21H2 development semester of Windows as a service, the commercial release of which is the original release of Windows 11. Work on Cobalt began in October 2020, although it did not replace Iron in the Dev Channel until December.
In March 2021, a refresh branch (co_refresh) was created as a part of the Sun Valley user experience refresh project. The new user interface was eventually merged to most branches, although notably excluding the public release branch (co_release) which still used the older Windows 10 user experience all the way up to build 21390 from May. The Dev Channel then remained on this build for four additional weeks while the new UI was being merged to the release branch. New builds resumed in June after the official announcement of Windows 11 with build 22000.51.
It was later followed by Nickel in the second half of 2021.
List of known builds[edit | edit source]
This list only includes client builds that were not compiled under the Sun Valley project, which was responsible for the Windows 11 user experience refresh. For Sun Valley builds, see Windows 11 (original release) § List of known builds. For server builds, see Windows Server, version 23H2 § List of known builds.
Available build Confirmed build Unconfirmed build Fake build Pre-Dev Channel[edit | edit source]
Dev Channel (rs_prerelease branch)[edit | edit source]
Dev Channel (co_release branch)[edit | edit source]
Notes[edit | edit source]
- ↑ Up to build 21390.2025.
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