Key Takeaways
- Microsoft released cumulative update KB5089573 on May 26, 2026 for Windows 11 versions 25H2 and 24H2.
- The update resolves a critical installation failure caused by insufficient free space (< 10 MB) on the EFI System Partition (ESP).
- Affected devices halted at ~35‑36 % during reboot with error code 0x800f0922.
- Prior temporary fixes included a Known Issue Rollback (KIR) and a registry‑based workaround (EspPaddingPercent).
- KB5089573 permanently eliminates the need for those workarounds.
- Besides the ESP fix, the update brings AI component refreshes (Image Search, Content Extraction, Semantic Analysis, Settings Model to v1.2605.856.0), personalization improvements, and a Servicing Stack Update (KB5092734, build 26100.8519).
- The update is available via Windows Update → Optional updates, the Microsoft Update Catalog, WSUS, or Windows Update for Business.
- Removal is possible through DISM commands; using wusa.exe / uninstall will not work because the Servicing Stack Update cannot be removed post‑install.
- Microsoft advises prioritizing KB5089573 in the next maintenance window due to its broad impact on consumer and enterprise devices.
Overview of KB5089573 and Its Primary Fix
Microsoft issued cumulative update KB5089573 on May 26, 2026 targeting Windows 11 versions 25H2 and 24H2. The update raises the OS builds to 26200.8524 (25H2) and 26100.8524 (24H2). Its chief purpose is to cure a widespread installation failure that appeared after the May 2026 Patch Tuesday security update (KB5089549). By addressing the underlying cause, KB5089573 restores the ability of affected systems to complete monthly security patches without manual intervention.
Root Cause: ESP Space Limitation and Error 0x800f0922
The failure traced back to devices with critically low free space on the EFI System Partition (ESP)—specifically, 10 MB or less available. During the update process, systems would progress through the initial installation phases but then crash at roughly 35‑36 % completion during the reboot phase, leaving the machine in an inconsistent state. The halt manifested as error code 0x800f0922, a symptom of the ESP lacking sufficient room for the update’s boot‑loader files and related metadata.
Temporary Workarounds: Known Issue Rollback and Registry Adjustment
Before a permanent fix, Microsoft provided two stopgap measures. First, a Known Issue Rollback (KIR) was automatically pushed to consumer and non‑managed business devices, reverting the offending components to a stable state. Second, enterprise administrators could apply a registry‑based workaround by adjusting the EspPaddingPercent value under HKLM\SYSTEM\CurrentControlSet\Control\Bfsvc. This tweak increased the reserved ESP padding, temporarily mitigating the space constraint until a formal update arrived.
Permanent Fix Delivered by KB5089573
KB5089573 supersedes both the KIR and the registry tweak, delivering a lasting solution. The update modifies the update engine’s handling of ESP allocation, ensuring that sufficient space is reserved regardless of the partition’s current free‑space level. Consequently, devices that previously stalled at 35‑36 % now complete the reboot phase successfully, and the error 0x800f0922 no longer appears. This permanent resolution removes the need for administrators to maintain workarounds.
AI Component Updates Included in the Cumulative Update
Beyond the ESP fix, KB5089573 refreshes several on‑device AI components to version 1.2605.856.0. The updated components include Image Search, Content Extraction, Semantic Analysis, and the Settings Model. These enhancements deepen Windows 11’s integrated AI capabilities, improving features such as contextual file suggestions, smarter search results, and more responsive system settings. Microsoft positions this refresh as part of its ongoing strategy to bring powerful AI processing directly to the client OS.
Personalization Enhancements and Servicing Stack Update
The cumulative update also adds personalization improvements that were introduced in the gradual rollout phase on May 28, 2026. While the release notes do not detail every tweak, users can expect refinements to themes, accent colors, and lock‑screen dynamics. Additionally, KB5089573 bundles a Servicing Stack Update identified as KB5092734, bringing the servicing stack to build 26100.8519. This SSU bolsters the reliability and robustness of the Windows update infrastructure itself, reducing the likelihood of future installation hiccups and ensuring smoother receipt of subsequent patches.
How to Obtain and Install KB5089573
The update is accessible through multiple channels with no special prerequisites beyond running a compatible Windows 11 25H2 or 24H2 device. Users can navigate to Start → Settings → Windows Update → Advanced options → Optional updates, locate KB5089573, and click Download and Install. Alternatively, IT professionals may download the standalone package directly from the Microsoft Update Catalog using the KB number. In enterprise environments, the update can be deployed via Windows Update for Business or WSUS, allowing administrators to stagger rollout or enforce compliance as needed.
Uninstallation Process and Recommendations Against Removal
Should removal become necessary, Microsoft advises using the DISM command line. First, run DISM /online /get-packages to identify the exact package name for KB5089573. Then execute DISM /Online /Remove-Package /PackageName:<package_name> where <package_name> corresponds to the LCU (Latent Cumulative Update) component. Notably, attempting to uninstall via the Windows Update Standalone Installer (wusa.exe /uninstall) will fail because the update bundles the Servicing Stack Update (SSU), which cannot be removed once applied. Microsoft strongly discourages removing security updates, as doing so re‑exposes systems to the vulnerabilities the patches were designed to mitigate.
Prioritizing the Update for Enterprise and Consumer Devices
Given the broad impact of the ESP space issue—affecting both consumer PCs and managed business workstations—Microsoft urges IT administrators and end users to prioritize KB5089573 during their next maintenance window. Applying the update not only eliminates the installation failure but also delivers AI enhancements, personalization refinements, and a more resilient servicing stack. By rolling out KB5089573 promptly, organizations can safeguard device stability, maintain security compliance, and take advantage of the latest AI‑driven features embedded in Windows 11.