Windows 10 build 21277

Windows 10 build 21277 is the first Insider Preview of Cobalt. It was released on 10 December 2020 to all Insiders on the Dev Channel along with Iron build 20277.

Features such as redesigned touch keyboard, emoji picker, voice typing, and theme-aware splash screens that were removed in Iron build 20246 have been reintroduced in this build. However, those that were only available to a small group of Insiders haven't been completely rolled out yet. The Meet Now integration on the Windows taskbar introduced in Iron build 20221 is now available for the Enterprise SKUs and Azure Active Directory (AAD) user accounts, where it was previously disabled.

x64 emulation has been added as a preview on ARM64 devices. Unlike WOW64 and the previous x86 emulation, the new emulator does not use a separate System directory with x64-compatible binaries. Instead, existing ARM64 binaries in  have been extended with x64-compatible code, using a new ARM64X machine type. The implementation in this build requires the user to download a preview version of the C++ runtime.

Changes

 * The new Microsoft Edge now comes preinstalled on upgraded machines, and it can't be uninstalled anymore.
 * Support for Unicode Emoji 12.1 and 13.0 has been added. They include over 200 new glyphs, a new gender-neutral design, and some existing emojis being redesigned.
 * The animations when opening and closing a window have been updated.
 * You can now use the Snip and Sketch app to create a screen snip and paste it directly into a folder of your choice in File Explorer to save the screenshot there. This change was initially added to the Beta Channel as part of the Feature Experience Pack update.
 * The legacy Snipping Tool is now an optional feature, and it can be uninstalled if preferred from Optional Features Settings.
 * The scaling logic of the graphs in Task Manager’s Performance tab has been adjusted.
 * Registry Editor dialog windows have been updated to support the Ctrl + Backspace key stroke to delete words.
 * The Start menu has been updated to display items at their parent folder's level if they are the only item in that folder.
 * The new Xbox app has replaced the previous Xbox Console Companion one.
 * Mixed Reality Portal's setup screens now feature a video showing a headset and some experiences.

Bugs

 * Some users might see a popup that says “Your PC ran into a problem and will restart in 1 min” after logging in to Windows with either an Azure Active Directory or Active Directory account. If encountered, save any data immediately and let the PC restart.
 * Live preview doesn't work for pinned site tabs on some machines.
 * The modern Disk Management page (Settings → System → Storage → Manage Disks and Volumes) in the Settings app is blank, as a result, it won't display any drives present. To workaround this issue, use the classic Disk Management tool to manage disk drives.

Availability
Starting with this build's release, the Dev Channel went under a temporary splitting of released builds. While the channel still received mandatory updates from the Iron development cycle, builds from this version would be released at the same time as optional updates, giving Insiders the ability to choose to keep receiving Iron builds or moving forward. For this case, the accompanying Iron build was 20277.