What's new in KB5124010 (Windows 11 build 26200.9550)
- Windows 11 version 25H2
- Windows 11 version 24H2
- OS Build 26200.9550
- OS Build 26100.9550
Priya Natarajan3 min readQuick answer
KB5124010 is an optional preview update released on September 22, 2026, for Windows 11 version 25H2 and version 24H2, bringing systems to OS Builds 26200.9550 and 26100.9550. As a non-security release, it delivers preliminary quality updates and fixes ahead of the upcoming monthly patch cycle. You can install it manually through Windows Update or download the standalone package directly from the Microsoft Update Catalog.
Microsoft has released KB5124010 as an optional non-security preview update for computers running Windows 11 version 25H2 and Windows 11 version 24H2. Released on September 22, 2026, this patch updates your system build numbers to OS Build 26200.9550 or OS Build 26100.9550 depending on the specific Windows 11 version running on your device. As an optional C-week preview update, this package serves as a testing ground for non-security updates and performance fixes before they are rolled into the mandatory cumulative update scheduled for the following month.
Understanding what is included in KB5124010 helps you decide whether you should update your PC today or wait for the automatic security updates later. This detailed guide covers everything you need to know about OS Build 26200.9550 and OS Build 26100.9550, including key highlights, known issues reported by Microsoft, update recommendations, and step-by-step instructions for getting the update installed on your device.
Highlights
- OS Build 26200.9550 update package introduced for systems running Windows 11 version 25H2.
- OS Build 26100.9550 preview package delivered for installations on Windows 11 version 24H2.
- Preview release model implementation giving early access to non-security fixes ahead of October releases.
- Microsoft Update Catalog package availability for manual installation and offline deployment.
- Windows Update channel integration under optional updates for user-initiated downloads.
Known issues
Microsoft reports no known issues for this update.
Should you install it?
Because KB5124010 is an optional preview release, most daily users do not need to install it immediately. Optional preview updates are primarily meant for enthusiasts, system administrators, and IT professionals who want to test incoming non-security improvements before they are formally deployed to all Windows 11 machines. If your PC is operating smoothly and you do not require immediate access to these servicing fixes, you can safely ignore this release. The changes included in this preview build will automatically be packaged into the compulsory security update on the next Patch Tuesday.
On the other hand, if you enjoy staying on the cutting edge of Windows 11 developments or need to verify operating system updates across managed hardware, installing KB5124010 is a great way to verify system stability on OS Build 26200.9550 or OS Build 26100.9550. If you encounter any unexpected behavior after installing preview updates, you can remove them using standard recovery options in Windows 11.
How to get it
Illustration: the Troubleshoot > Other troubleshooters page under Settings > System
Installing KB5124010 is straightforward and can be accomplished either through the Windows Update menu in Settings or by downloading the standalone file from the Microsoft Update Catalog.
To check for and install the update via Windows Settings:
- Open the Settings app by navigating to Settings > Windows Update or pressing the Windows key + I shortcut.
- Toggle on the option labeled Get the latest updates as soon as they're available if you wish to receive preview releases promptly.
- Click the Check for updates button at the top of the window.
- Wait for Windows Update to scan for available updates until September 22, 2026—KB5124010 (OS Builds 26200.9550 and 26100.9550) Preview appears in the list.
- Click Download and install next to the update listing.
- Allow the download and installation to complete, then click Restart now when prompted to reboot your computer.
If you prefer to download the update manually for offline installation or deployment across multiple computers:
- Open your web browser and visit the Microsoft Update Catalog website.
- Type KB5124010 into the search bar at the top right and press Enter.
- Locate the package corresponding to your operating system version, such as Windows 11 version 25H2 or version 24H2.
- Click the Download button next to the relevant build.
- Double-click the downloaded .msu file on your system to launch the standalone installer.
- Follow the on-screen installation prompts and restart your device when finished.
To verify that the update installed successfully, go to Settings > System > About and check under Windows specifications to ensure your OS build reflects OS Build 26200.9550 or OS Build 26100.9550. If the installation stalls or fails, you can run the Windows Update troubleshooter in Settings > System > Troubleshoot > Other troubleshooters to identify and fix common update errors. Alternatively, administrators can manage update packages through PowerShell or Command Prompt scripts, though running command-line servicing tools should always be handled with caution to prevent accidental system configuration issues.
Sources
Frequently asked questions
Is KB5124010 a mandatory update for Windows 11?
No, KB5124010 is an optional non-security preview update. You only need to install it if you want early access to fixes before the next mandatory monthly update.
What OS builds does KB5124010 update your system to?
KB5124010 updates Windows 11 version 25H2 systems to OS Build 26200.9550 and Windows 11 version 24H2 systems to OS Build 26100.9550.
Are there any known issues with KB5124010?
Microsoft reports no known issues for KB5124010 at this time.
How can I check if KB5124010 is installed on my computer?
Go to Settings > System > About and check your OS build number under Windows specifications. If it reads 26200.9550 or 26100.9550, KB5124010 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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