Windows 11 KB5124010 (Build 26200.9550): September 2026 Preview Update

Quick Answer

KB5124010 is a September 2026 cumulative preview update for Windows 11 versions 25H2 and 24H2. On Windows 11 25H2, it takes the operating system to Build 26200.9550; Windows 11 24H2 receives Build 26100.9550. Microsoft released the update on September 22, 2026.

The update contains a mixture of new Windows features, gradual-rollout improvements, and non-security quality fixes. Notable changes include File Explorer improvements, Emoji 17.0, additional precision-touchpad gestures, Copilot-key remapping, Bluetooth improvements, a new accessibility option to open apps maximized, and improvements to Windows Recovery Environment.

What Is KB5124010?

KB5124010 is a preview cumulative update, rather than the regular monthly security update. Microsoft describes it as containing production-quality improvements and distributes some features through a gradual rollout, meaning that individual features may not appear on every eligible PC immediately.

For Windows 11:

This article focuses particularly on Windows 11 25H2 Build 26200.9550.

What's New in KB5124010?

File Explorer Improvements

KB5124010 introduces several File Explorer changes.

For files downloaded from the web, the Preview pane now provides a Preview anyway option for HTML files after the user acknowledges the warning. Other files, including PDFs, can now be previewed automatically.

Other File Explorer improvements include:

• File Explorer Home remembers whether sections were expanded or collapsed.
• Cloud-file thumbnail previews in the Details pane become more reliable.
• The Details pane has been reorganized to make file properties easier to review.
• An issue that could clear the address-bar contents while entering edit mode has been addressed.

Emoji 17.0 Support

The update adds support for Emoji 17.0, including new emoji characters.

The existing emoji designs have also received refinements for greater consistency.

Users can open the Windows emoji panel with:

Windows + .

New Tips Widget

Windows 11 now includes a Tips widget that provides short guidance about Windows features.

It can be added from the Widgets board using Add widgets > Tips. Microsoft also provides the option to add Tips to supported lock-screen widget configurations.

Bluetooth Improvements

KB5124010 includes several Bluetooth reliability and compatibility improvements.

Among the changes are:

• Better visual feedback when changing Bluetooth Classic Audio volume.
• More accurate Bluetooth connection status.
• Improved stability of the Bluetooth and devices settings page.
• A fix for a situation where the Bluetooth radio could be turned off while its Settings toggle incorrectly remained on.
• Improved microphone compatibility with certain Bluetooth Classic Audio devices.
• A fix for a Bluetooth audio streaming crash associated with error code 0x139.
• Reliability and performance improvements for LE Audio.
• Improvements to shared audio.

New Accessibility Setting: Open Apps Maximized

A new accessibility option called Open apps maximized automatically maximizes application windows as they open.

The setting is available under:

Settings > Accessibility > Visual effects > Open apps maximized

Microsoft describes the feature as useful for users who prefer applications to consistently open in a maximized state, including some accessibility and tablet-mode scenarios.

Magnifier Improvements

The Magnifier taskbar receives a visual refresh.

Microsoft has updated:

• Toolbar icons
• Spacing and padding
• Overall visual consistency with Windows 11

Existing Magnifier views, zoom controls, keyboard shortcuts, and Read Aloud behavior remain unchanged.

Additional Precision Touchpad Gestures

KB5124010 adds additional gesture options for supported precision touchpads.

The new controls include:

• Single-finger scrolling from the left or right side of the touchpad.
• Automatic scrolling, which continues scrolling when the finger is moved toward the touchpad edge.

The update follows earlier touchpad gesture improvements delivered in the July 2026 update.

Copilot Key Remapping

Windows 11 now provides a setting that allows the dedicated Copilot key on supported keyboards to be remapped.

The key can be configured to function as:

• Right Ctrl
• Context Menu

This can help users who prefer traditional keyboard functions or specific accessibility workflows.

Camera Roll Backup

The update introduces Camera roll backup in Windows Settings for eligible users.

The feature can help protect photos through OneDrive. Microsoft notes that availability depends on the device and market. Setup can be initiated from supported Settings pages and completed using a QR code on a mobile phone.

Windows Recovery Environment Improvements

WinRE, or Windows Recovery Environment, receives an important networking improvement.

Windows can now automatically reuse eligible Wi-Fi profiles already saved on the PC, including supported certificate-based networks. This can allow supported recovery scenarios to connect to Wi-Fi without manually preconfiguring credentials in WinRE.

The update also adds a recovery remote-management plug-in intended to extend WinRE management capabilities for MDM providers.

Windows Backup and PC-to-PC Migration

Microsoft has removed the PC-to-PC Migration feature from Windows Backup.

For moving supported files and settings from an old PC to a new Windows PC, Microsoft directs users toward Windows Backup instead.

Other Changes

KB5124010 also contains improvements involving:

• Desktop backgrounds and personalization.
• DIB image files as desktop backgrounds.
• Desktop slideshow reliability.
• Multiple-desktop slideshow wallpapers.
• Installed-app version information in Settings.
• Time-format handling in Settings.
• Camera settings persistence.
• Windows fonts, including additional Ebrima script support.
• Kiosk-mode keyboard shortcuts.
• Laptop power/battery state detection.

Quality and Reliability Fixes

The normal rollout portion of KB5124010 addresses several issues.

Camera

The update addresses a problem that could cause the built-in camera to stop working in the Camera application and other applications using the camera.

File History

Microsoft fixes an issue in which File History could fail to back up or restore files to an external drive or network location.

Affected systems could incorrectly display a "Reconnect your drive" message even when the backup drive was properly connected and functioning.

System Monitor (Sysmon)

Several Sysmon problems are addressed, including:

• Executable-header validation issues involving malformed or truncated files.
• A file-system filter driver problem that could cause a stop error.
• Incorrect Event ID 25 process-tampering alerts involving smss.exe.

Servicing Stack Update Included

KB5124010 includes KB5124009, a servicing stack update associated with Build 26100.9539.

Servicing stack updates improve the reliability of the Windows update installation process.

Known Issues in KB5124010

Domain-Joined PCs and Secure Trust Relationships

Microsoft currently lists an issue affecting some domain-joined devices with Credential Guard-protected machine accounts.

After the September 8, 2026 security update or later updates, some systems can lose their secure channel with an on-premises Active Directory domain. Affected users may see a message indicating that the trust relationship between the device and the domain failed.

The issue is associated with Machine Identity Isolation configurations. Microsoft states that the feature is supported only in environments connected to domain controllers running at Windows Server 2025 Domain Functional Level (DFL) or later.

This is particularly relevant for organizations managing domain-joined Windows PCs.

Microsoft provides workarounds involving Intune, Group Policy, or registry configuration, followed by restarting the device and repairing the computer's secure channel.

Because registry and domain configuration changes can affect authentication and system connectivity, administrators should follow Microsoft's documented procedure rather than making unrelated registry changes.

USB Audio Class 1.0 Devices

Microsoft also lists an issue affecting some USB Audio Class 1.0 devices.

Possible symptoms include:

• Device Manager showing Code 10.
• No audio output.
• Unresponsive volume controls.
• Sound settings becoming unavailable or unresponsive.

Microsoft states that this issue is limited to USB Audio Class 1.0 devices and that a resolution is being worked on.

Should You Install KB5124010?

KB5124010 is a preview update, so users should distinguish it from the normal monthly security release.

For a typical home or office PC that is working correctly, there is usually no need to install a preview update simply because it is available. Users who specifically want the newly released features or need one of the included fixes can consider installing it after checking compatibility.

For business or domain-managed systems, administrators should pay particular attention to Microsoft's currently documented domain-trust issue before broadly deploying the update.

How to Check Whether KB5124010 Is Installed

Open:

Settings > Windows Update > Update history

Look for:

2026-09 Cumulative Update Preview for Windows 11 Version 25H2 for x64-based Systems (KB5124010)

You can also verify the Windows build by pressing:

Windows + R

and entering:

winver

For Windows 11 25H2, the expected build after installing this update is 26200.9550.

How to Install KB5124010

For normal Windows users, Microsoft provides the update through Windows Update.

Go to:

Settings > Windows Update > Advanced options > Optional updates

If KB5124010 is offered, it can be selected and installed from there.

Microsoft also provides the update through the Microsoft Update Catalog for supported deployment scenarios.

For enterprise deployment or offline installation, administrators should use Microsoft's documented installation procedure and ensure that any required checkpoint cumulative updates are installed in the required order.

Important Note for Windows 11 24H2 Users

Microsoft states that Windows 11 24H2 Home and Pro editions reach end of updates on October 13, 2026. Enterprise and Education editions remain supported until October 12, 2027.

Therefore, organizations and users running 24H2 should consider their Windows-version lifecycle separately from the question of whether to install KB5124010.

Frequently Asked Questions

Is KB5124010 a security update?

KB5124010 is a cumulative preview update containing quality improvements and new features. It is not the regular monthly security release.

What build does KB5124010 install?

On Windows 11 25H2, KB5124010 takes the system to Build 26200.9550. On Windows 11 24H2, it results in Build 26100.9550.

Is KB5124010 available for Windows 11 25H2?

Yes. Microsoft lists KB5124010 as applying to Windows 11 25H2 and 24H2.

Does KB5124010 add Emoji 17.0?

Yes. Microsoft lists Emoji 17.0 support among the gradual-rollout features in the update.

Can the Copilot key be remapped after this update?

Yes, on supported devices. KB5124010 introduces a Windows 11 setting that can remap the Copilot key to Right Ctrl or the Context Menu key.

Does the update improve Bluetooth?

Yes. Microsoft lists multiple Bluetooth reliability, compatibility, audio, microphone, and connection-state improvements.

Are there known problems with KB5124010?

Microsoft currently documents issues involving some domain-joined systems with Machine Identity Isolation and some USB Audio Class 1.0 devices.

Can I install KB5124010 manually?

Yes. Microsoft provides the update through the Microsoft Update Catalog as well as Windows Update. Manual deployment has additional requirements for checkpoint cumulative updates and architecture-specific packages.

Conclusion

Windows 11 KB5124010 is the September 2026 preview cumulative update for Windows 11 25H2 and 24H2. For 25H2, it brings the operating system to Build 26200.9550 and introduces or improves features across File Explorer, Bluetooth, accessibility, touchpad gestures, the Copilot key, Windows Recovery, personalization, and other Windows components.

Because it is a preview release and Microsoft has documented known issues, organizations should evaluate it against their hardware, drivers, domain configuration, and business applications before broad deployment.

Sources

• Microsoft Support — September 22, 2026—KB5124010 (OS Builds 26200.9550 and 26100.9550) Preview — Microsoft Support
• Microsoft Learn — Windows 11 Insider Release Preview Build 26100.9539/26200.9539 — Microsoft Learn