Microsoft Support:
This cumulative update for Windows 11, version 26H1 (KB5124012) includes the latest security fixes and improvements, along with non-security updates from last month's optional preview release. Visit the Windows release health dashboard for the latest status on this release.
Improvements
This update includes new features and quality improvements that were part of the following update:The following summary outlines key quality improvements addressed by this update. The bold text within the brackets indicates the item or area of the change.
- [Security updates] This update provides security improvements. For more information about the security vulnerabilities resolved by this update, see the Security Update Guide
- [Secure Boot] This update includes additional high confidence device targeting data, increasing coverage of devices eligible to automatically receive new Secure Boot certificates. Certificate deployment via Windows updates continues across supported PCs and non-managed business devices in the coming months.
- [Teams and Outlook on Arm64 PCs] Fixed: This update addresses an issue that could cause Microsoft Teams and Microsoft Outlook to unexpectedly close on Arm64-based PCs.
- [Date and Time] This update adjusts Morocco Standard Time to reflect Morocco's transition to permanent UTC+00:00 effective September 20, 2026. This change ensures that the correct local time is displayed after the transition.
- [Remote Desktop Audio Redirection] This update addresses an issue affecting Remote Desktop audio redirection that could prevent audio from a remote session from playing on the local device in certain configurations.
- [OMA-DM Client Logging] This update improves diagnostic logging for the OMA-DM client by adding certificate chain information for server connections, helping administrators troubleshoot device management connectivity issues.
Component updates
AI componentsThis release updates the following AI components to version 1.2608.951.0: Image Search, Content Extraction, Semantic Analysis, and Settings Model.
To learn more, see Release information for AI components.
Servicing stack update
Includes KB5125104 (Build 28000.2950), which improves the reliability of the Windows update installation process. To learn more about SSUs, see [Simplifying on-premises deployment of servicing stack updates](https://learn.microsoft.com/windows/deployment/update/servicing-stack-updates#simplifying-on-premises-deployment-of-servicing-stack-updates).
Known issues in this update
Microsoft is not currently aware of any issues with this update.How to get this update
Before you install this update
Microsoft combines the latest servicing stack update (SSU) for your operating system with the latest cumulative update (LCU). For general information about SSUs, see Servicing stack updates.Deployment
If you deploy dynamic updates such as this update to an existing Windows image, ensure the boot.stl file is included as part of the installation media. Failure to include the file might prevent devices from successfully starting from the installation media and can result in error code 0xc0430001.Note: The boot.stl file is used during Secure Boot validation and must match the Windows version and architecture of the image you are updating.
To ensure the boot.stl file is included as part of the installation media, do one of the following:
- Use the Update WinPE script to update an existing Windows image. (Recommended)
- Manually copy the boot.stl file from the device Windows\Boot\EFI folder to the corresponding folder on your installation media before deploying the update.
Install this update
To install this update, use one of the following Windows and Microsoft release channels.| Available | Next Step |
|---|---|
| This update downloads and installs automatically from Windows Update and Microsoft Update. |
|
| Before you install this update, the standalone package(s) for this update is available from the Microsoft Update Catalog website. This update contains MSU files that require installation in a specific order. You can install this update using Method 1 (install all MSU files together) or Method 2 (install each MSU file individually, in order) in the Arm64 installation instructions section. Note: This latest cumulative update includes updates for AI components. Even though the AI component updates are included in the update, the AI components are only applicable to Windows Copilot+ PCs and will not install on Windows PC or Windows Server. |
File information
For a list of the files provided in this update, download the file information for cumulative update KB5124012.For a list of the files provided in the servicing stack update, download the file information for the SSU (KB5125104) - version 28000.2950.
Source:
September 8, 2026-KB5124012 (OS Build 28000.2954) | Microsoft Support
September 8, 2026-KB5124012 (OS Build 28000.2954)
support.microsoft.com
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