kb5128942

KB5128942 is a Windows 11 cumulative update that applies only to the out-of-box experience, the setup phase a new or reset PC goes through before anyone reaches the desktop. According to the tagged discussion, Microsoft released it on September 22, 2026 for Windows 11 versions 24H2 and 25H2, and it downloads and installs automatically while a device is being set up and connected to the internet, restarting before setup continues. It replaces the earlier KB5122035 OOBE package from August. The tag is most relevant to people setting up or resetting PCs and to those building deployment images, since the update changes the Windows code a device runs during setup rather than after normal installation.