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KB5120998 Not Installing or Stuck in Windows 11

Affects
  • Windows 11, version 25H2 (OS Build 26200.9278)
  • Windows 11, version 24H2 (OS Build 26100.9278)
Maya Reyes4 min read

Quick answer

KB5120998 is an optional preview update for Windows 11 versions 24H2 and 25H2. If it becomes stuck during download or fails to install, you can resolve the issue by running the Windows Update troubleshooter, clearing the SoftwareDistribution cache folder, or running SFC and DISM scans. Because KB5120998 is a non-security preview release, you can also safely pause or skip the update until next month.

On this page

Microsoft released KB5120998 on August 27, 2026, as an optional preview update for devices running Windows 11, version 24H2 and Windows 11, version 25H2. Installing this update advances systems on version 24H2 to OS Build 26100.9278 and devices on version 25H2 to OS Build 26200.9278. Microsoft offers preview updates late in the month to allow users to test non-security fixes before they become mandatory.

However, some Windows 11 users experience issues where KB5120998 gets stuck at various downloading percentages or fails with an error code. Installation freezes and download errors typically happen when cached update files become corrupted, required background update services stop responding, or system files block the installation process. The following steps will help you resolve the installation issue or bypass the update safely.

Method 1: Run the Windows Update troubleshooter

When to use: Use this as your initial step when KB5120998 stops progressing during download or installation.

  1. Open the Start menu and select Settings (or press Windows Key + I).
  2. In the left navigation bar, select System, then scroll down on the right side and click Troubleshoot.
  3. Click Other troubleshooters to view the list of built-in diagnostics.
  4. Find Windows Update in the list and click the Run button next to it.
  5. Allow the diagnostic tool to run, identify background service glitches, and apply automatic fixes.

What to expect afterwards: After the troubleshooter finishes, restart your PC, go back to Settings > Windows Update, and click Check for updates to retry downloading KB5120998.

Method 2: Clear the SoftwareDistribution cache folder

When to use: Use this method if KB5120998 repeatedly fails to install or stays stuck at the exact same percentage, which indicates corrupted temporary update files.

  1. Click the Start button, type "cmd", right-click Command Prompt, and select Run as administrator.
  2. In the command window, type net stop wuauserv and press Enter to halt the primary update service.
  3. Type net stop bits and press Enter to stop the Background Intelligent Transfer Service.
  4. Press Windows Key + R to open the Run box, enter C:\Windows\SoftwareDistribution, and press Enter.
  5. Select all files and folders inside the SoftwareDistribution directory (Ctrl + A) and delete them.
  6. Return to the Administrator Command Prompt, type net start wuauserv and press Enter, then type net start bits and press Enter to restart both services.

What to expect afterwards: Windows will rebuild the cache directory. Re-open Windows Update to trigger a fresh download of KB5120998.

Method 3: Reset Windows Update components

When to use: Try this deeper reset if standard troubleshooting and clearing the cache folder fail to resolve persistent installation errors for KB5120998.

  1. Open the Start menu, search for Command Prompt, right-click it, and select Run as administrator.
  2. Stop all core update services by entering the following commands one by one, pressing Enter after each:
    • net stop wuauserv
    • net stop cryptSvc
    • net stop bits
    • net stop msiserver
  3. Rename the system cache folders by running these commands:
    • ren C:\Windows\SoftwareDistribution SoftwareDistribution.old
    • ren C:\Windows\System32\catroot2 catroot2.old
  4. Restart the update services by executing these commands one by one:
    • net start wuauserv
    • net start cryptSvc
    • net start bits
    • net start msiserver
  5. Close the Command Prompt window and restart your computer.

What to expect afterwards: Windows rebuilds its update infrastructure upon reboot, clearing configuration conflicts blocking OS Build 26100.9278 or OS Build 26200.9278.

Method 4: Run SFC and DISM system repair tools

When to use: Use this method if missing or damaged Windows system files prevent KB5120998 from completing its installation.

  1. Right-click the Start menu button and select Terminal (Admin) or Command Prompt (Admin).
  2. Type DISM.exe /Online /Cleanup-image /Restorehealth and press Enter to repair the Windows system component store.
  3. Allow the DISM scan to complete fully, which may take up to 15 to 20 minutes.
  4. Type sfc /scannow and press Enter to scan for damaged system files.
  5. Once the System File Checker completes its verification and repairs, restart your computer.

What to expect afterwards: System file integrity will be restored, allowing Windows Update to apply KB5120998 without file corruption errors.

Method 5: Pause or skip the KB5120998 Preview update

When to use: Choose this option if KB5120998 continues to stall and you prefer not to continue troubleshooting an optional preview update.

  1. Press Windows Key + I to open Settings.
  2. Click Windows Update in the left navigation pane.
  3. Locate the Pause updates section under More options.
  4. Click the Pause for 1 week button to temporarily halt incoming updates.
  5. Leave the update uninstalled and resume normal computer usage.

What to expect afterwards: Your device will stop attempting to download KB5120998. Because KB5120998 is an optional preview release, Microsoft says all non-security fixes included in this update will automatically be included in the next mandatory monthly security update.

If nothing worked

If none of the above solutions resolve the issue with KB5120998, your PC may have specific software conflicts. Because KB5120998 was released on August 27, 2026, as an optional preview update for OS Builds 26200.9278 and 26100.9278, skipping it carries no security risks. You can wait for the upcoming compulsory cumulative update or use official Windows 11 installation media to perform an in-place upgrade, which repairs operating system files without removing your personal files or installed applications.

Frequently asked questions

Is KB5120998 a mandatory update for Windows 11?

No, KB5120998 is an optional preview update released on August 27, 2026. You can safely skip it without exposing your device to security risks.

Which Windows 11 builds are updated by KB5120998?

KB5120998 applies to Windows 11 version 24H2 (updating to OS Build 26100.9278) and version 25H2 (updating to OS Build 26200.9278).

What should I do if KB5120998 is stuck downloading at 0% or 99%?

Run the Windows Update troubleshooter or clear the SoftwareDistribution folder to delete corrupted download files and force Windows to retry.

Will I lose fixes if I skip the KB5120998 preview update?

No, all non-security quality fixes included in preview updates are rolled into the following month's mandatory cumulative update.

Verified: pending — this guide is awaiting a hands-on check on a current build.

Written by

Maya Reyes

Maya writes Thea's update coverage. She tracks every Windows 11 cumulative and feature update on the day it ships, installs it on a test PC, and reports what changed and what to watch for. Placeholder bio — replace before launch.

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