Hotpatch for Windows Server
Hotpatching is a way to install OS security updates on Windows Server without having to restart your machine. Hotpatching patches the in-memory code of running processes without the need to restart the process. Hotpatching also provides the following benefits:
Fewer binaries mean updates install faster and consume less disk and CPU resources.
Lower workload impact with less need to restart your machine.
Better protection, as the Hotpatch update packages are scoped to Windows security updates that install faster without requiring you to restart your machine.
Reduces the time exposed to security risks and change windows, and easier patch orchestration with Azure Update Manager.
Supported platforms
Azure and Azure Stack HCI virtual machines
The following table lists the exact combinations of publisher, OS offer, and SKU that support Hotpatching for Windows Server 2022 and Windows Server 2025 on Azure. Virtual machines (VMs) you create on Azure Stack HCI using these combinations also support Hotpatching.
Note
Windows Server container base images, custom images, or any other combination of publisher, offer, and SKU aren't supported.
Not all regions currently support Windows Server 2025: Azure Edition images. If you try to use this feature in a region that doesn't currently support Windows Server 2025: Azure Edition, you might see an HTTP 400 client error. To work around this issue, use a different region that does currently support this feature, such as UK South, East Asia, or West Central US.
| Publisher | OS Offer | SKU |
|---|---|---|
| MicrosoftWindowsServer | WindowsServer | 2022-Datacenter-Azure-Edition-Core |
| MicrosoftWindowsServer | WindowsServer | 2022-Datacenter-Azure-Edition-Core-smalldisk |
| MicrosoftWindowsServer | WindowsServer | 2022-Datacenter-Azure-Edition-Hotpatch |
| MicrosoftWindowsServer | WindowsServer | 2022-Datacenter-Azure-Edition-Hotpatch-smalldisk |
| MicrosoftWindowsServer | WindowsServer | 2025-Datacenter-Azure-Edition |
| MicrosoftWindowsServer | WindowsServer | 2025-Datacenter-Azure-Edition-smalldisk |
| MicrosoftWindowsServer | WindowsServer | 2025-Datacenter-Azure-Edition-Core |
| MicrosoftWindowsServer | WindowsServer | 2025-Datacenter-Azure-Edition-Core-smalldisk |
For more information about the available images, see Windows Server on the Azure Marketplace.
Azure Arc-connected machines (preview)
Important
Azure Arc-enabled Hotpatch is currently in PREVIEW. See the Supplemental Terms of Use for Microsoft Azure Previews for legal terms that apply to Azure features that are in beta, preview, or otherwise not yet released into general availability.
Azure Arc-connected Windows Server 2025 machines can receive Hotpatches if you enable the feature on Azure Arc Portal. To start using Azure Arc-enabled Hotpatch, connect Azure Arc to machines using one of the following editions:
Windows Server 2025 Datacenter Edition
Windows Server 2025 Standard Edition
How Hotpatch works
Hotpatch first establishes a baseline with the current Cumulative Update for Windows Server. Every three months, the baseline periodically refreshes with the latest Cumulative Update. You then receive Hotpatch releases for the next two months after the Cumulative Update. For example, if January is a Cumulative Update, February and March would have Hotpatch releases. For more information about the Hotpatch release schedule, see Release notes for Hotpatch in Azure Automanage for Windows Server 2022.
There are two types of baselines: Planned baselines and Unplanned baselines.
Planned baselines are released on a regular cadence, with Hotpatch releases in between. Planned baselines include all the updates in a comparable Latest Cumulative Update for that month and require you to restart your machine.
- For example, a planned one year release period may include four planned baseline releases in a calendar year and eight Hotpatch releases.
Unplanned baselines are released during an unplanned important update, such as a zero-day fix, when that particular update can't be released as a Hotpatch. When unplanned baselines release, a Hotpatch release is replaced with an unplanned baseline for that month. Unplanned baselines also include all the updates in a comparable Latest Cumulative Update for that month, and therefore require you to restart your machine.
- Because these events are unplanned, developers can't predict unplanned baselines in advance.
Hotpatch updates don't require you to restart your machine. Because Hotpatches patch the in-memory code of running processes without needing to restart them, your applications aren't affected. This lack of restarting doesn't affect the performance or functionality implications of the patch itself.
Supported updates
Hotpatch covers Windows Security updates and maintains parity with the content of security updates issued to in the regular non-Hotpatch Windows update channel.
There are a few important things you need to consider when enabling Hotpatch on a supported version of Windows Server. You still need to restart your machine to install updates that aren't included in the Hotpatch program. You also need to periodically restart after installing a new baseline. Restarting keeps your VM in sync with non-security patches included in the latest cumulative updates.
The following patches currently aren't included in the Hotpatch program and require you to update your machine during Hotpatch release months:
Non-security updates for Windows
.NET updates
Non-Windows updates, such as drivers, firmware updates, and so on.
Patch orchestration process
Hotpatch is an extension of Windows Update and typical management processes. However, the kinds of tools Hotpatch uses for patch management vary depending on which platform you're using.
Azure
VMs you create in Azure using a supported Windows Server image have Automatic VM Guest Patching enabled by default.
Hotpatch automatically downloads and applies patches classified as Critical or Security to your VM.
Hotpatch applies patches during off-peak hours in the VM time zone.
Azure manages patches for you, applying patches according to availability-first principles.
Azure monitors VM health through platform health signals to detect patching failures.
Note
You can't create VM scale sets (VMSS) with Uniform orchestration on Azure Edition images with Hotpatch. To learn more about which features are supported by Uniform orchestration for scale sets, see A comparison of Flexible, Uniform, and availability sets.
Azure Stack HCI
Azure Stack HCI can orchestrate Hotpatch updates for VMs using the following tools:
Group Policy configures Windows Update client settings.
SCONFIG configures Windows Update client settings for Server Core.
Third-party patch management solutions.
Azure Arc-connected machines
Azure Arc-connected machines can install and manage Hotpatch updates using the following tools:
Azure Update Manager
Group Policy configures Windows Update client settings.
SCONFIG configures Windows Update client settings for Server Core.
Third-party patch management solutions.
For more information about which tools Hotpatch uses, check out our Azure Update Manager documentation.
Understand the patch status for your VM in Azure
To view the patch status for your VM, open the Overview page for your VM in the Azure portal. From there, under Operations, select Updates. You should see the patch status and most recently installed patches under Recommended updates.
In the Recommended updates page, you can see the Hotpatch status of your VM and if there are any available patches for your VM. As we stated in How Hotpatch works, Automatic VM Guest Patching automatically installs all Critical and Security patches on your VM.
Patches outside of those two categories aren't automatically installed, and are instead displayed in the Update compliance tab as a list of available patches. You can also check the Update history tab to view patch installation details for update deployments on your VM from the past 30 days.
Automatic VM Guest Patching regularly runs assessments of available patches, which you can view in the Updates tab. You can manually start an assessment by selecting the Assess Now button. You can also install patches on-demand by selecting the Install updates now button. This option lets you choose whether to install all updates under specific patch classifications or select individual updates to include or exclude by providing a list of knowledge base articles. However, keep in mind that patches you install manually don't follow availability-first principles and might require you to restart your VM.
You can also view installed patches by running the Get-HotFix cmdlet in PowerShell or by viewing the Settings menu in Desktop Experience.
Rollback support for Hotpatching
Hotpatch updates don't support automatic rollback. If you experience an issue during or after an update, you must uninstall the latest update and install the last functional baseline update. This process requires that you restart the VM.