KB5124010 not installing or stuck in Windows 11
- Windows 11, version 26H2
- Windows 11, version 25H2
- Windows 11, version 24H2
- OS Build 26300.9550
- OS Build 26200.9550
- OS Build 26100.9550
Maya Reyes5 min readQuick answer
If KB5124010 fails to install or gets stuck during download, run the built-in Windows Update troubleshooter from Settings. If that does not resolve the issue, resetting the Windows Update services and clearing the download cache will usually force the update to complete. Because KB5124010 is an optional preview update, you can also pause updates until the next mandatory release.
Microsoft released KB5124010 on September 22, 2026, as a preview update for Windows 11 version 24H2, Windows 11 version 25H2, and Windows 11 version 26H2. Depending on which version of Windows 11 you run, installing this package brings your operating system to OS Build 26100.9550, OS Build 26200.9550, or OS Build 26300.9550. However, standard updates sometimes fail to finish, getting stuck at specific percentages such as 20%, 99%, or throwing generic error codes during restart.
Update installation failures happen for several ordinary reasons. Windows Update files can become corrupted during download, background services may hang, or existing system files might prevent the installer from registering changes. If KB5124010 fails to install or gets stuck on your PC, follow the step-by-step methods below to repair the update process and complete the installation.
Method 1: Run the Windows Update troubleshooter
Illustration: the Troubleshoot > Other troubleshooters page under Settings > System
Use this method first whenever an update fails or freezes during download. The automated troubleshooter scans core update components, checks background services, and applies automatic fixes for standard update errors.
- Open the Start menu and click on the Settings gear icon (or press Windows key + I on your keyboard).
- Stay on the System tab in the left panel, then scroll down on the right side and click Troubleshoot.
- Click Other troubleshooters to view the full list of available diagnostic tools.
- Locate Windows Update near the top of the list and click the Run button next to it.
- Wait for the automated scan to check service statuses and repair pending update flags. If the tool identifies issues, it will apply the fix automatically.
- Close the troubleshooter window, restart your computer, and return to Settings > Windows Update to check for updates again.
After completing these steps, Windows Update should attempt a clean download of KB5124010 without hanging on previous error states.
Method 2: Clear the SoftwareDistribution download cache
Illustration: the Windows Update page in Windows 11 Settings
Use this method if KB5124010 gets stuck downloading at a specific percentage or fails repeatedly with file download errors. Windows stores update files temporarily in a folder named SoftwareDistribution. If any file in this cache is damaged, the update installer will hang indefinitely.
- Open the Start menu, type cmd, right-click Command Prompt, and select Run as administrator.
- In the Command Prompt window, type
net stop wuauservand press Enter to stop the Windows Update service. - Type
net stop bitsand press Enter to stop the Background Intelligent Transfer Service. - Press Windows key + R to open the Run dialog box, type
C:\Windows\SoftwareDistribution, and press Enter. - Select all files and folders inside the SoftwareDistribution directory (press Ctrl + A), then press Delete to move them to the Recycle Bin (or permanently delete them).
- Return to your administrator Command Prompt window, type
net start wuauservand press Enter. - Type
net start bitsand press Enter to restart the required services. - Restart your computer and check for updates under Settings > Windows Update.
Clearing this directory forces Windows to download a completely fresh copy of the KB5124010 installation files.
Method 3: Reset Windows Update services using Command Prompt
Use this method if clearing the cache alone did not resolve the problem, or if Windows Update displays persistent error codes. Resetting the catalog and network sockets restores default settings across all update sub-components.
- Open the Start menu, type cmd, right-click Command Prompt, and choose Run as administrator.
- Stop the core update services by entering the following commands one by one, pressing Enter after each:
net stop wuauservnet stop cryptSvcnet stop bitsnet stop msiserver
- Rename the update cache folders by typing
ren C:\Windows\SoftwareDistribution SoftwareDistribution.oldand pressing Enter, then typingren C:\Windows\System32\catroot2 catroot2.oldand pressing Enter. - Reset the network socket configuration by typing
netsh winsock resetand pressing Enter. - Restart the services by typing the following commands one by one, pressing Enter after each:
net start wuauservnet start cryptSvcnet start bitsnet start msiserver
- Close Command Prompt and restart your PC.
When Windows boots back up, open Settings > Windows Update and select Check for updates to start a clean installation of KB5124010.
Method 4: Run the System File Checker and DISM tools
Use this method if you suspect underlying system file corruption is preventing Windows 11 OS Build 26100.9550, 26200.9550, or 26300.9550 from registering update files correctly. The System File Checker (SFC) and Deployment Image Servicing and Management (DISM) tools inspect and repair system component stores.
- Click the Start menu, type cmd, right-click Command Prompt, and select Run as administrator.
- Type
DISM.exe /Online /Cleanup-image /Restorehealthand press Enter. - Wait for the DISM scan to complete. This process may take 10 to 15 minutes depending on your system configuration.
- Once DISM finishes, type
sfc /scannowand press Enter. - Allow the System File Checker to scan all protected system files and replace corrupted files automatically.
- Reboot your PC when the scan completes, then open Settings > Windows Update and click Check for updates.
After the system image and system files are validated, KB5124010 should install without hitting file-lock errors.
If nothing worked
If KB5124010 continues to fail after trying all methods, keep in mind that KB5124010 is an optional preview update released on September 22, 2026. Preview updates are non-security packages designed to let users test upcoming fixes ahead of schedule. They are not mandatory for keeping your computer secure.
You can safely skip this update by opening Settings > Windows Update and selecting Pause updates for 1 week. Microsoft will include all fixes contained within KB5124010 in the next mandatory Patch Tuesday update, which will install automatically when released.
Sources
Frequently asked questions
Is KB5124010 a mandatory update for Windows 11?
No, KB5124010 is an optional preview update released on September 22, 2026. Your PC remains secure even if you choose not to install it.
Why does KB5124010 get stuck downloading at 99%?
Updates usually freeze at high percentages when temporary installation files inside the SoftwareDistribution cache are damaged or locked by background services. Resetting update services or clearing the cache resolves this stall.
What OS builds are associated with KB5124010?
KB5124010 applies to Windows 11 versions 24H2, 25H2, and 26H2, updating systems to OS Build 26100.9550, OS Build 26200.9550, or OS Build 26300.9550.
Checked against Microsoft's release notes on ; re-checked when a new build ships.
Covers Windows 11 update releases and the problems that follow them. Tracks Microsoft's release-health notes daily and flags known issues the same day they appear.
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