Windows 10 build 21387 (co_release)

Build of Cobalt
OS familyWindows 10 (NT 10.0)
Version number10.0
Build number21387
Build revision1
Architecturex86, x64, ARM64
Build labco_release
Compiled on2021-05-18
Expiration date
Timebomb2021-10-31 (+166 days)
Home (China, N, Single Language)
Cloud (N)
Pro (China Only, N, Single Language)
Pro Education (N)
Pro (N) for Workstations
Education (N)
Enterprise (N, (N) Evaluation, G (N))
Enterprise multi-session
IoT Enterprise
About dialog
21387 winver.png
TCB.png TCBGallery.png

Windows 10 build 21387 (co_release) is the nineteenth Insider Preview build of Cobalt, the 21H2 development semester of Windows as a service. This build was released on 21 May 2021 to all Windows Insiders on the Dev Channel.

Changes[edit | edit source]

  • Internet Explorer 11's functionality has been disabled and attempting to run its executable file (iexplore.exe) will open Edge instead. It is still possible to run Internet Explorer if ieframe.dll is replaced with a copy from an older build.
  • The "Eco mode" experimental Task Manager feature introduced in build 21364 has been removed.
  • The first log-in has been updated to use smaller and Segoe UI Variable text, though the flashing animation is still kept.

Bugs[edit | edit source]

News and interests[edit | edit source]

  • The flyout might occasionally flash in the screen's top left corner when opened.

Camera Settings[edit | edit source]

  • The Camera app does not respect the brightness adjustments made to a camera under its respective page.

Installation[edit | edit source]

  • The update process to this build has a chance of hanging for extended periods of time.
  • Some devices might fail to upgrade to this build with error code 0xc1900101 due to a second issue different from that in build 21382.

OOBE[edit | edit source]

  • The OOBE may use an incorrect font when this build is ran under Simplified Chinese language pack.

General[edit | edit source]

  • Certain parts of Search, including the File Explorer search box, are not displaying correctly in the dark theme.
  • The icons for Microsoft Edge and File Explorer in the taskbar are swapped in clean installations.

Gallery[edit | edit source]

External links[edit | edit source]