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 Portuguese language for the x64 architecture. As of 2023, the English language version of this build remains to be found.

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.

Internet Explorer 11

 * Internet Explorer has been updated to version 11.0.2.
 * The "Tabs" button has been added to Metro IE.

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.