[BUG] Cowork fails on Windows 11 25H2 — vmflexio.sys driver missing from standard distribution

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Cowork fails to start the VM with HRESULT 0x80070003 ("path not found") on "Microsoft Flexible IO Device".

The driver vmflexio.sys is completely absent from C:\Windows\System32\drivers\ on Windows 11 25H2 (Build 26200.8039). This has been verified on TWO separate machines running 25H2 — the file does not exist on either.

Error message:
HCS operation failed: failed to start VM: HcsWaitForOperationResult failed with HRESULT 0x80070003
"Microsoft Flexible IO Device: failed to power on with error 'The specified path was not found' (0x80070003)"

Attempted fixes (none restore the file):

• sfc /scannow
• DISM /Online /Cleanup-Image /RestoreHealth
• Full Hyper-V uninstall/reinstall
• Enabling Containers feature
• All Hyper-V sub-components enabled (Hypervisor, Services, Tools)

Verification:
Test-Path "C:\Windows\System32\drivers\vmflexio.sys" → False (on both machines)

This is NOT a per-machine corruption issue — vmflexio.sys is simply not shipped with Windows 11 25H2.

OS: Windows 11 Pro 25H2 (Build 26200.8039)
Claude Desktop: latest version

What Should Happen?

Cowork should start the VM successfully. The vmflexio.sys driver should be present or Cowork should not depend on a driver that is not included in Windows 11 25H2.

Error Messages/Logs

Impossible de démarrer l'espace de travail de Claude.
HCS operation failed: failed to start VM: HcsWaitForOperationResult failed with HRESULT 0x80070003: {"Error":-2147024893,"ErrorMessage":"Le chemin d’accès spécifié est introuvable.","ErrorEvents":[{"Message":"Échec du démarrage de « cowork-vm-0258427d ». (ID d’ordinateur virtuel DE945451-B195-5B31-8FEB-CF32E6C7DF56)","Provider":"51ddfa29-d5c8-4803-be4b-2ecb715570fe","EventId":12030,"Flags":13,"Data":[{"Type":"String","Value":"cowork-vm-0258427d"},{"Type":"String","Value":"DE945451-B195-5B31-8FEB-CF32E6C7DF56"}]},{"Message":"« cowork-vm-0258427d » Microsoft Flexible IO Device (ID d’instance C4B741F5-5582-4C98-8F8B-2E082933C396) : échec de la mise sous tension avec l’erreur « Le chemin d’accès spécifié est introuvable. » (0x80070003). (ID d’ordinateur virtuel DE945451-B195-5B31-8FEB-CF32E6C7DF56)","Provider":"51ddfa29-d5c8-4803-be4b-2ecb715570fe","EventId":12010,"Flags":5,"Data":[{"Type":"String","Value":"cowork-vm-0258427d"},{"Type":"String","Value":"DE945451-B195-5B31-8FEB-CF32E6C7DF56"},{"Type":"String","Value":"Microsoft Flexible IO Device"},{"Type":"String","Value":"%%2147942403"},{"Type":"String","Value":"0x80070003"},{"Type":"String","Value":"C4B741F5-5582-4C98-8F8B-2E082933C396"},{"Type":"String","Value":""}]}],"Attribution":[{"OperationFailure":{"Detail":"Start"}},{"VirtualDeviceFailure":{"Detail":"PowerOnCold","Name":"Microsoft Flexible IO Device","DeviceId":"a8679153-843f-467f-ad7e-f429328f7568","InstanceId":"c4b741f5-5582-4c98-8f8b-2e082933c396"}}]}
Redémarrer Claude ou votre ordinateur résout parfois ce problème. Si cela persiste, vous pouvez réinstaller l’espace de travail.

Steps to Reproduce

1. Install Windows 11 Pro 25H2 (Build 26200.8039)
2. Enable all Hyper-V features (Hypervisor, Services, Tools, Virtual Machine Platform, Hypervisor Platform)
3. Install Claude Desktop (latest version)
4. Open Cowork tab
5. VM fails immediately with HRESULT 0x80070003 on "Microsoft Flexible IO Device"
6. Verify: Test-Path "C:\Windows\System32\drivers\vmflexio.sys" → False

Reproduced on two separate machines running Windows 11 25H2.

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

No, this is a new issue

Claude Code Version

Claude Desktop (latest, Windows Store version)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

This is a Claude Desktop Cowork issue, not Claude Code CLI.

vmflexio.sys is missing from the standard Windows 11 25H2 distribution. Verified on two separate machines (both Build 26200.8039, Windows 11 Pro). Neither sfc /scannow nor DISM /RestoreHealth can restore the file because it was never included in 25H2.

Cowork's VM depends on a driver that does not ship with the current stable version of Windows 11.