What's new in KB5129195 (Windows 11 build 26200.9457)
- Windows 11 version 24H2
- Windows 11 version 25H2
- Build 26200.9457
- Build 26100.9457
Priya Natarajan3 min readQuick answer
KB5129195 is an out-of-band update released on September 14, 2026, for Windows 11 version 24H2 and version 25H2. It advances systems to OS Build 26200.9457 and Build 26100.9457 to address key fixes following the previous update cycle. You can download it directly through Windows Update or from the Microsoft Update Catalog.
Microsoft released KB5129195 as an out-of-band update on September 14, 2026. This cumulative update is available for systems running Windows 11 version 24H2 and Windows 11 version 25H2. Installing this package bumps the operating system build numbers to OS Build 26100.9457 for version 24H2 and OS Build 26200.9457 for version 25H2.
Out-of-band releases are special updates that arrive outside Microsoft's standard Patch Tuesday schedule. While monthly cumulative updates like KB5124008 arrived on September 8, 2026 (updating devices to OS Builds 26200.9445 and 26100.9445), an out-of-band release like KB5129195 is published when specific fixes need to reach devices quickly. If you are running Windows 11 version 24H2 or version 25H2, this update affects your system.
Understanding what is inside KB5129195 helps you determine how and when to deploy it across your devices. Below, you will find the documented changes, install instructions, and details on how to check your current OS build number.
Highlights
- Increments the operating system build version for Windows 11 version 25H2 to OS Build 26200.9457.
- Increments the operating system build version for Windows 11 version 24H2 to OS Build 26100.9457.
- Delivers an out-of-band servicing update published on September 14, 2026.
- Follows and builds upon the updates previously included in KB5124008 (OS Builds 26200.9445 and 26100.9445).
- Updates core servicing stack and system components for Windows 11 version 24H2 and version 25H2.
Known issues
Microsoft reports no known issues for this update.
Should you install it?
Because KB5129195 is an out-of-band update, Microsoft publishes it to resolve specific issues that require immediate attention rather than waiting for the next regular monthly update window. If your PC is experiencing stability issues or if you want your system completely up to date with the latest OS Build 26200.9457 or Build 26100.9457 release, you should install this package.
If your current build (such as OS Build 26200.9445) is working without any problems and your device is managed in a strict enterprise environment, you might choose to test the update on a single test device before deploying it broadly. However, for most home users and daily productivity PCs, installing out-of-band servicing releases promptly is recommended to keep your device secure and aligned with the latest Windows 11 servicing branch.
How to get it
Illustration: the Troubleshoot > Other troubleshooters page under Settings > System
To check your current build number before or after updating, navigate to Settings > System > About and look under Windows specifications for the OS build value.
Method 1: Windows Update
- Open the Start menu and select Settings.
- Click on Windows Update in the left navigation pane.
- Click the Check for updates button on the top right.
- Wait for Windows Update to search for available releases.
- When KB5129195 appears, click Download and install.
- Restart your computer when prompted to complete the installation.
If you run into issues during the download or installation process, you can run the Windows Update troubleshooter by going to Settings > System > Troubleshoot > Other troubleshooters and selecting Run next to Windows Update.
Method 2: Microsoft Update Catalog
If you prefer to download the standalone package manually or install it on an offline PC, you can use the Microsoft Update Catalog route.
- Open your web browser and navigate to the official Microsoft Update Catalog website.
- In the search box, type KB5129195 and press Enter.
- Locate the file matching your system architecture and Windows 11 version (24H2 or 25H2).
- Click the Download button next to the package.
- Open the downloaded .msu package file to launch the standalone installer.
- Follow the on-screen prompts and restart your device when finished.
Caution: Downloading manual packages requires selecting the exact architecture for your processor. Installing an incorrect update file will fail or cause installation errors. Always verify your system type under Settings > System > About before manually installing standalone packages.
Alternative PowerShell method
For advanced users who prefer command-line options, you can check installed package details using PowerShell.
- Right-click the Start button and select Terminal (Admin) or Windows PowerShell (Admin).
- Type
Get-HotFix -Id KB5129195and press Enter.
Caution: Modifying system packages or running administrative management commands can affect system behavior. Ensure you save all open work before executing elevated system routines.
Sources
Frequently asked questions
What build number does KB5129195 bring Windows 11 to?
KB5129195 updates Windows 11 version 25H2 to OS Build 26200.9457 and Windows 11 version 24H2 to OS Build 26100.9457.
Is KB5129195 an out-of-band update?
Yes, KB5129195 is an out-of-band update released on September 14, 2026, outside the standard monthly Patch Tuesday schedule.
How can I verify if KB5129195 is installed?
Go to Settings > System > About and check your OS build number. If it displays 26200.9457 or 26100.9457, the update is successfully installed.
Checked against Microsoft's release notes on ; re-checked when a new build ships.
Writes Thea's how-to guides for new and changed Windows 11 features: where a setting moved, how to turn it on or off, and what it actually does. Every guide is checked against Microsoft's release notes and updated when a new build changes the steps.
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