Missing preview update22,26 KB5124010

Install the latest cumulative update available for Windows 11 24H2 or 25H2—KB5124010 itself is not required if a newer cumulative update is available—then install Windows 11 26H2 from Windows Update.

The update number in the question appears mistyped: the prerequisite is KB5124010, not KB124010. It applies to Windows 11 24H2, 25H2, and 26H2.^1^

Install the prerequisite

1. Open Start → Settings → Windows Update.
2. Select Check for updates.
3. Install every available cumulative update, including a newer October or November 2026 cumulative update if offered.
4. Restart the computer.

A later cumulative update satisfies the 26H2 prerequisite, so there is no need to locate the September preview separately.^2^

If no cumulative update appears:

1. Open Settings → Windows Update → Advanced options → Optional updates.
2. Install KB5124010 if listed.
3. Restart Windows.

If KB5124010 is not offered

Download it manually from the Microsoft Update Catalog.^3^

1. Determine the installed architecture under Settings → System → About → System type.
2. In the catalog, select the package matching:
   • Your current version: Windows 11 24H2 or 25H2
   • Your architecture: x64 for most PCs or ARM64 for ARM-based PCs
3. Download all MSU files shown as required for that entry.
4. Place them together in an otherwise empty folder.
5. Install any checkpoint cumulative updates first, in the order shown by the catalog, and install the target cumulative update last.
6. Restart the PC.

Do not choose the 26H2 package when the computer is still running 24H2 or 25H2.

Install Windows 11 26H2

After installing KB5124010 or a later cumulative update:

1. Open Settings → Windows Update.
2. Select Check for updates.
3. When Windows 11, version 26H2 is available appears, select Download & install.
4. Restart when prompted.

The 26H2 enablement package is KB5121794. It supports upgrades from Windows 11 24H2 or 25H2, requires KB5124010 or later, and is delivered through Windows Update rather than the Microsoft Update Catalog.^2^

After restarting, press Windows+R, enter winver, and confirm that the displayed version is 26H2.

References

1. September 22, 2026—KB5124010 (OS Builds 26300.9550, 26200.9550, and ...
2. KB5121794: Feature update to Windows 11, version 26H2 by using an ...
3. Microsoft Update Catalog