Windows Server 2025 is Microsoft"s latest version of the server SKU. Typically, when customers upgrade from an older version of Windows Server to a newer one like Windows Server 2025, they either perform a clean install or an in-place upgrade, usually via physical installation media. However, Microsoft has recently opened another in-place upgrade path.
Earlier this month, Microsoft began offering IT admins the option to perform an in-place upgrade to Windows Server 2025 via Windows Update. This upgrade path facilitates users who want to quickly perform in-place upgrades without relying on physical media. The Redmond tech giant has assured customers that "most" applications and services will continue to work well after you upgrade, but it does strive for 100% compatibility.
In order to properly plan your migration, Microsoft recommends defining maintenance windows, configuring Group Policy correctly, checking if you need a product key, validating activation with your organization"s KMS, and ensuring that you have enough free space. Once you have done all of this, you can follow the steps outlined here to modify your Windows Registry and trigger the update mechanism.
Microsoft has discouraged performing this in-place upgrade on a Domain Controller (DC). These endpoints should instead be upgraded to Windows Server 2025 through a clean install. The Redmond tech giant has also encouraged IT admins to first configure a test environment to ensure that they follow the update process correctly. Once that is vetted, they should begin upgrading, starting with the least critical servers. On average, the snapshot and update process should take around two hours per server, but it is highly dependent on your deployment"s performance and the number of applications and users leveraging it.
Once the in-place upgrade is complete, you should follow the post-installation steps listed below:
After installation and reboot, check that the applications and services are running correctly. If there are any issues, restore the server from backup/snapshot.
Activate the server using one of the following activation methods: KMS, Active Directory‑based Activation, or MAK using slgmr or VAMT tools.
Check Telemetry settings and any Loopback Adapter settings.
After the server is confirmed to be working, the Windows.old directory can be deleted to free up space on the system drive.
Check Windows Update for additional updates.
Evaluate if Secured-core settings and UEFI Secure Boot certificates should be updated.
https://techcommunity.microsoft.com/blog/windowsservernewsandbestpractices/opt-in-windows-server-2025-feature-update-from-the-ws-2022-and-ws-2019-settings-/4515961
