Windows 8.1 build 9600.16581

Windows 8.1 build 9600.16581 is a build of Windows 8.1 Update 1, which was shared on 4 January 2021 only in the Brazilian Portugese language for the x64 architecture. As of 2022, the English language version of this build remains to be found.

History
Prior to being shared, Russian website WZor.Net released an article describing the build in question on 8 January 2014, where seven images of its English language version were posted alongside others on Twitter. On 13 January, another screenshot of this build was posted on the Polish language CentrumWindows forum.

New features

 * Internet Explorer has been updated to version 11.0.2.

Bugs and quirks

 * In the Brazilian Portuguese version, the Microsoft Confidential watermark uses pseudolocalized text.
 * Most update packages that a user installs on this build will cause the system to enter recovery mode.