KB5089549, the May 2026 cumulative for Windows 11 24H2 and 25H2, downloads and stages cleanly then dies on install with 0x800f0922. Microsoft confirmed the known issue on May 21. Root cause is the EFI System Partition running below the 260 to 300 MB free space the servicing stack needs to stage boot files.

HP EliteBook 840 G7 and G8 fleets are taking the hit hardest, with Dell Latitude and several Surface generations close behind. The shared pattern is machines that shipped with a 100 MB ESP and have absorbed five years of cumulative updates.

Check ESP Free Space First

Open an elevated PowerShell. Mount the ESP to a temporary letter, read free bytes, then unmount.

mountvol Z: /S
Get-PSDrive Z | Select-Object Used, Free
mountvol Z: /D

Under 100 MB free and you have the bug. Under 250 MB and you are close enough to hit it on the next cumulative.

Expand the EFI System Partition

The supported path is diskpart plus a partition mover. Back up the machine first. This rewrites partition boundaries.

Boot from Windows 11 install media. Choose Repair, then Command Prompt. Identify the disk and ESP:

diskpart
list disk
select disk 0
list partition

Shrink the OS partition by 200 MB to free space adjacent to the ESP, then extend the ESP into it. Microsoft covers the full process for MBR and GPT layouts in their UEFI/GPT partition guide.

If the OS partition is not adjacent to the ESP, you need a third-party tool like MiniTool Partition Wizard or AOMEI to move partitions safely. Test on one machine before rolling fleet-wide.

Quick Triage Script

Worth running across your managed endpoints this week. Pipe ESP free space to your RMM and flag anything under 200 MB before next Patch Tuesday.

$drive = "Z:"
mountvol $drive /S
$free = (Get-PSDrive Z).Free
mountvol $drive /D
"$env:COMPUTERNAME ESP free: $([math]::Round($free/1MB,1)) MB"

Need help auditing EFI partitions across your fleet before the next update cycle? Rain City Techworks handles managed IT and security for businesses in the Seattle and Tacoma area.