Microsoft published the optional Windows 11 preview update KB5127936 on October 28, 2026, for versions 25H2 and 26H2. It includes Cloud Rebuild, a full Windows reinstall that runs from the Windows Recovery Environment (WinRE). The feature is rolling out in phases, and it requires working WinRE, supported hardware, a compatible network driver and internet access. It also erases local files, accounts, apps and settings. (Microsoft’s release notes; Cloud Rebuild requirements)
What KB5127936 changes
Microsoft lists KB5127936 as an optional preview for Windows 11 25H2 and 26H2, with OS builds 26300.9818 and 26200.9818. The release notes do not map each build number to a specific version. Because the rollout is phased, including Cloud Rebuild in the update does not mean the feature is already visible on every PC.
This follows NeoTeo’s earlier coverage of Cloud Rebuild’s preview-stage features. The October update adds a choice to request data sanitization through storage hardware before reinstalling Windows.
Cloud Rebuild reinstalls Windows and removes local data
Cloud Rebuild downloads a Windows image and device drivers from Windows Update, then reinstalls Windows through WinRE. It does not preserve the existing local installation: the process reformats the system disk and removes local files, accounts, apps and settings. Microsoft says cloud-stored files, such as OneDrive content, are not affected. (Microsoft Learn)
The sanitize option requests an erase operation from the storage hardware. Microsoft says the result depends on the drive’s capabilities and implementation, and Windows cannot independently verify what the hardware did. The operation is irreversible, so it is intended for situations such as returning, reassigning or retiring a drive, not a routine reinstall.
Microsoft also warns users to keep the PC connected to power and not interrupt preparation, downloading, installation or sanitization. Interrupting the process can leave Windows unable to boot.
What must work for the rebuild to start
A PC that cannot start Windows may enter WinRE after repeated boot failures, but Cloud Rebuild still needs a healthy WinRE environment. The PC must meet Windows 11’s minimum hardware requirements, WinRE must have a compatible network driver, and it must be able to reach the internet. (Microsoft’s Cloud Rebuild guidance)
Microsoft documents Ethernet or WPA-Personal Wi-Fi as connection options. WinRE can also reuse compatible saved Wi-Fi profiles, including supported certificate-based networks. Without a working recovery environment or internet connection, the cloud download and reinstall cannot proceed.
How Cloud Rebuild differs from Quick Machine Recovery
Cloud Rebuild downloads Windows and performs a full reinstall, removing local data. Quick Machine Recovery takes a different route: after repeated boot failures, it searches Windows Update for a targeted fix. Microsoft describes Quick Machine Recovery as best-effort, so it may not find a remedy for every problem. (Windows device recovery framework; Quick Machine Recovery)
For a widespread boot outage such as the CrowdStrike incident, Microsoft provided a separate incident-specific recovery tool and identifies Quick Machine Recovery in its broader recovery framework for mass-scale boot outages. Cloud Rebuild is a general reinstall path with data-loss consequences and WinRE requirements, rather than that incident-specific tool.
