What's new in KB5134133 (Windows 11 build 26300.9725)
- Windows 11 version 26H2
- Windows 11 version 25H2
- Windows 11 version 24H2
- OS Build 26300.9725
- OS Build 26200.9725
- OS Build 26100.9725
Maya Reyes4 min readQuick answer
KB5134133 is an out-of-band servicing update released by Microsoft on October 26, 2026, for Windows 11 versions 26H2, 25H2, and 24H2. It updates systems to OS Builds 26300.9725, 26200.9725, and 26100.9725 respectively. The update delivers targeted platform maintenance across all three supported Windows 11 branches.
Microsoft released KB5134133 on October 26, 2026, as an out-of-band servicing update for Windows 11. Unlike standard monthly updates that arrive on Patch Tuesday, out-of-band releases are distributed outside the normal release cadence to address specific operational needs or deliver critical updates across operating system branches. This update applies directly to three active versions of Windows 11: version 26H2, version 25H2, and version 24H2.
Depending on which version of Windows 11 your machine is running, applying KB5134133 will update your system build to OS Build 26300.9725, OS Build 26200.9725, or OS Build 26100.9725. For everyday Windows users, keeping track of these build numbers is a helpful way to confirm that your device has successfully received the latest platform maintenance.
Understanding Out-of-Band Releases
Out-of-band updates serve a specific purpose in Microsoft's Windows servicing model. While regular monthly updates deliver security patches and non-security enhancements on a predictable schedule, out-of-band updates are published when Microsoft identifies improvements that require immediate deployment across devices. Because KB5134133 affects multiple Windows 11 feature releases simultaneously, users on version 24H2, version 25H2, and version 26H2 will see their OS build numbers increment accordingly.
If you are unsure which build your PC is currently running, you can easily verify it in Settings under System, then About. Matching your OS build against OS Build 26300.9725, OS Build 26200.9725, or OS Build 26100.9725 confirms that KB5134133 is fully installed on your device.
Highlights
- Delivers an out-of-band servicing update specifically for Windows 11 version 26H2, updating the system build to OS Build 26300.9725.
- Provides out-of-band servicing changes for Windows 11 version 25H2, advancing the system build to OS Build 26200.9725.
- Applies out-of-band system maintenance to Windows 11 version 24H2, bringing the system build to OS Build 26100.9725.
- Released on October 26, 2026, as a cumulative out-of-band patch across all three supported Windows 11 version branches.
- Updates underlying Windows core components simultaneously for devices across Windows 11 24H2, 25H2, and 26H2 releases.
Known issues
Microsoft reports no known issues for this update.
Should you install it?
Out-of-band updates like KB5134133 are designed to maintain platform reliability across all supported versions of Windows 11. Because this update applies to Windows 11 version 26H2, version 25H2, and version 24H2, most users will benefit from keeping their devices current with Microsoft's latest servicing updates. If your device receives updates automatically through Windows Update, the package will download and install without requiring manual intervention beyond a routine system restart.
If you manage devices in a home office or small business environment where system uptime is critical, applying out-of-band releases promptly ensures your devices run the most up-to-date operating system builds. However, if you prefer to schedule updates around specific working hours, you can use the built-in pause features in Windows Update to delay installation until a convenient time. Overall, because Microsoft reports no known issues with KB5134133, there is no immediate reason to hold back on updating your device.
How to get it
Illustration: the Troubleshoot > Other troubleshooters page under Settings > System
KB5134133 can be acquired through automatic updates via Windows Update or installed manually using the Microsoft Update Catalog.
Getting the update through Windows Update:
- Click the Start button on your taskbar and select the Settings icon, or press Windows key + I on your keyboard.
- In the Settings window, click on Windows Update from the left-hand navigation pane.
- Click the Check for updates button to initiate a manual check for available packages.
- When KB5134133 appears in the list of available updates, select Download & install.
- Allow the download to complete, then click Restart now when prompted to finish applying the build update.
Downloading from the Microsoft Update Catalog:
- Launch your web browser and navigate to the official Microsoft Update Catalog website.
- Located in the upper right section of the site, enter KB5134133 into the search query box and click Search.
- Review the search results list to identify the package matching your specific Windows 11 version, such as OS Build 26300.9725 for version 26H2, OS Build 26200.9725 for version 25H2, or OS Build 26100.9725 for version 24H2.
- Click the Download button beside the appropriate package entry, then click the download link in the pop-up window to save the installer file to your computer.
- Double-click the downloaded file to run the standalone installer, follow the prompts, and restart your computer when prompted.
If you encounter issues during installation, running the standard Windows Update troubleshooter in Settings under System, then Troubleshoot, can help resolve common update delivery conflicts.
Sources
Frequently asked questions
What is KB5134133 in Windows 11?
KB5134133 is an out-of-band update released by Microsoft on October 26, 2026, for Windows 11 versions 26H2, 25H2, and 24H2. It provides system updates and bumps operating system build numbers.
What build numbers does KB5134133 update to?
Depending on your Windows 11 version, KB5134133 updates your system build to OS Build 26300.9725 (version 26H2), OS Build 26200.9725 (version 25H2), or OS Build 26100.9725 (version 24H2).
Are there any known issues with KB5134133?
Microsoft reports no known issues for this update, making it safe for general installation.
How can I install KB5134133 manually?
You can download the standalone update for KB5134133 directly from the Microsoft Update Catalog by searching for KB5134133 and picking the file for your Windows 11 version.
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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