Windows 11 24H2/25H2: September 2026 KB5124008 and later updates

KB5124008 delivered builds 26100.9445 and 26200.9445 on September 8, 2026. Insider previews should not be mistaken for features confirmed in the stable update.

September 8 release

Microsoft released KB5124008 for Windows 11 24H2 and 25H2, builds 26100.9445 and 26200.9445 respectively. It is a cumulative security update delivered automatically through Windows Update according to device settings. Its official release page does not identify generally available movable taskbars, Start menu sizes or the search controls claimed by the earlier article.

Taskbar and Start in Insider previews

During spring 2026 Microsoft demonstrated top and side taskbar positions, a smaller taskbar and Start controls including section visibility and hiding the account name and photo in Windows Insider channels. A preview announcement does not mean these features reached all PCs through KB5124008. Availability and settings can vary by build and phased rollout; check the installed build notes.

Later fixes and known issues

Microsoft subsequently released KB5129195 on September 14, preview KB5124010 on September 22 and KB5127648 on October 13, 2026. Its notes describe issues including File History and, in some enterprise environments, lost domain trust, with resolutions described in the respective update pages. Avoid assigning unspecified vulnerability totals or unlisted features to KB5124008.

Check your PC

Open Settings > Windows Update > Update history, or run winver to inspect version and build. Install the latest cumulative update appropriate for your device, subject to organizational policy and Microsoft’s current known-issues notes. Do not install an old KB as if it were the newest.

Version support

As of October 14, 2026, Windows 11 24H2 Home and Pro received their final monthly update on October 13 and have reached end of updates. Enterprise and Education have different support dates. Plan a move to a supported version for Home/Pro machines. Features do not necessarily reach 24H2 and 25H2 devices simultaneously.

Microsoft sources

KB5124008: https://support.microsoft.com/en-us/servicing/os/windows-11/2026/09/kb5124008-windows-11-24h2-25h2-security-update ; KB5124010: https://support.microsoft.com/en-us/servicing/os/windows-11/2026/09/kb5124010-windows-11-24h2-25h2-update ; KB5127648: https://support.microsoft.com/en-us/servicing/os/windows-11/2026/10/kb5127648-windows-11-24h2-25h2-26h2-security-update ; Insider: https://blogs.windows.com/windows-insider/2026/05/15/improving-windows-quality-making-taskbar-and-start-more-personal/ .