KB5102951

Microsoft has released cumulative update KB5102951 (build 28120.2387) for Windows 11 Insider Program participants on the Experimental channel. This build belongs to version 26H1 and contains a number of significant changes aimed at increasing interface customization flexibility, as well as special features for the education sector. The main focus of the build is on modernizing the taskbar, which now supports changing its screen position and a new compact display mode for devices with small displays. Additionally, insiders received fixes for issues related to File Explorer and the Outlook app.

• Taskbar position change. Users can now change the position of the taskbar on the screen. In Settings → Personalization → Taskbar → Taskbar behaviors, a choice of screen side is available: bottom, top, left, or right. In any position, tooltips, menus, and animations correctly appear from the side of the taskbar. Most appearance settings, including the smaller taskbar and Never combine taskbar buttons mode, work in all positions. Support for touch gestures, the search box, and the Ask Copilot feature in alternative positions is still being refined. Auto-hide taskbar and the tablet-optimized version are not yet supported.
• Smaller taskbar. The ability to use a smaller taskbar has been added to free up additional screen space, which is especially relevant for compact devices. In this mode, icons become smaller, and the height of the bar itself is reduced. Core elements such as Start, Search, and the notification area scale while maintaining alignment and a unified visual style. Size control is carried out via the Show smaller icons on the taskbar option in Settings → Personalization → Taskbar → Taskbar behaviors. When Always is selected, both the icons and the height of the bar are reduced. Work is underway to further simplify resizing in settings.
• Free upgrade to Windows 11 Pro for educational institutions (K-12). Insiders in K-12 educational environments can now upgrade from Windows 11 Home to the Windows 11 Pro for Education edition for free and in a one-way manner. This allows educational institutions to purchase devices with the Home version of the system and centrally update them for transfer to corporate management. To start the upgrade, you need to log in with a local account, run the command prompt as an administrator, execute the Clipupgrade.exe command and authorize with a K-12 organization account to confirm the upgrade right. The system will prepare the update and complete it after a restart. Reverting to Windows 11 Home without a clean reinstall is not supported.

As part of fixing known issues, Microsoft resolved an error that caused the OneDrive shortcut in File Explorer to stop functioning when launching the file manager with administrator privileges. Also fixed is an issue with the Outlook app, which last week might not have responded to pressing the close button. No other major documented issues have been identified in this build.

To install update KB5102951, you need to go to Settings → Windows Update and click the Check for updates button. The build will be downloaded and installed automatically; a computer restart is required to complete the process.

It should be remembered that this build is intended exclusively for Windows Insider Program participants on the Experimental channel of version 26H1 and contains changes that are still in the stage of active refinement, including incomplete support for touch gestures for alternative taskbar positions.

How the new features work:

Taskbar Position Change. The system processes the registry parameter and the shell window orientation property, dynamically recalculating the bounding box of the bar and altering the menu flyout animation vectors. When selecting a side in Settings → Personalization → Taskbar → Taskbar behaviors, the visual tree of XAML islands is rebuilt, adjusting the binding of tooltips, jump lists, and touch indicators to the corresponding screen edge without restarting the explorer.exe process.

Smaller Taskbar. The feature modifies the icon placement grid style in Taskbar.dll, applying alternative layout resources with a reduced row height value and a decreased icon scale in the ImageList. The Show smaller icons on the taskbar toggle switches a boolean variable, forcing the renderer to recalculate the interactive area sizes of the Start button, search, and tray while maintaining center alignment without altering the core window grouping logic.

Free Upgrade to Windows 11 Pro for Educational Institutions. The process employs the targeted licensing mechanism Clipupgrade.exe, which performs a one-way migration of the EditionID registry key and replaces the Microsoft-Windows-Editions-Professional branding package in the CBS component store. The utility validates the K-12 activation key via the cloud licensing service, initiates the installation of a deferred provisioning package, and commits the ProductPolicy branch, blocking reversion to Home without a clean partition reinstall.

Fixes for Known Issues (OneDrive and Outlook). A security token collision was resolved where the File Explorer process, launched with elevated privileges in a different integrity context (High Mandatory Level), lost the ability to interact with the OneDrive namespace integration point in the folder tree root, causing navigation events to be ignored. The Outlook fix restores correct processing of the WM_CLOSE message in the main window's message loop, preventing the session termination command from being ignored.

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