[BUG] Cowork "Virtualization is not available" on Windows 11 Enterprise Build 26200 — yukonSilver classified as unsupported despite all prerequisites met

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 displays "Virtualization is not available — Claude's workspace requires Hyper-V, but the virtualization service isn't responding. Restart your computer to resolve this."

The Cowork enablement process gets stuck at 95% and then fails with Error code 1.

A full clean reinstall (removing MSIX package, old Squirrel remnants, VM bundles, logs, CoworkVMService, HNS networks, and temp files) did not resolve the issue. The yukonSilver detection bug reappears immediately after fresh installation.

What Should Happen?

Expected Behavior

Cowork should detect that Hyper-V is fully enabled and all virtualization services are running on Windows 11 Enterprise, successfully download the VM bundle, and launch the workspace.

Actual Behavior

Claude Desktop's internal platform classifier marks this system as yukonSilver not supported (status=unsupported), which prevents the VM bundle from ever being downloaded. The enablement process stalls at 95% and fails with exit code 1.

Error Messages/Logs

From `%LOCALAPPDATA%\Packages\Claude_pzs8sxrjxfjjc\LocalCache\Roaming\Claude\logs\cowork_vm_node.log`:


[info] [cleanupVMBundleIfUnsupported] yukonSilver not supported (status=unsupported), checking for stale bundle...


This entry repeats on every launch. The VM bundle is never downloaded. The `vm_bundles` directory is never created.

Steps to Reproduce

1. Install Claude Desktop v1.1.7714.0 from claude.com/download on Windows 11 Enterprise x64 (Build 26200)
2. Ensure all virtualization features are enabled (Hyper-V, VMP, WHP)
3. Confirm all services running (vmcompute, vmms, CoworkVMService)
4. Launch Claude Desktop
5. Click the Cowork tab
6. Observe: Enablement gets stuck at 95%, fails with Error code 1
7. Observe: "Virtualization is not available" error

Claude Model

Opus

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

2.1.78 (Claude Code)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Terminal.app (macOS)

Additional Information

Expected Behavior

Cowork should detect that Hyper-V is fully enabled and all virtualization services are running on Windows 11 Enterprise, successfully download the VM bundle, and launch the workspace.

Actual Behavior

Claude Desktop's internal platform classifier marks this system as yukonSilver not supported (status=unsupported), which prevents the VM bundle from ever being downloaded. The enablement process stalls at 95% and fails with exit code 1.

Troubleshooting Already Attempted

• ❌ Full clean reinstall (removed MSIX package, Squirrel remnants, VM bundles, logs, temp files, CoworkVMService, HNS networks)
• ❌ Fresh download from claude.com/download, installed as Administrator
• ❌ Verified all Hyper-V features enabled via Get-WindowsOptionalFeature
• ❌ Confirmed bcdedit hypervisorlaunchtype set to Auto
• ❌ No VPN active
• ❌ No Docker, WSL2, or other VM conflicts
• ❌ Multiple reboots

Additional Notes

• Regular Chat mode works perfectly. Only Cowork is affected.
• This appears to be the same yukonSilver classification issue reported in #25034, #25136, #27316, #27357, #29532, #30997, #32004, #32280, and #32574.
• The growthbook feature flag system loads on startup, suggesting the "unsupported" status may be server-side rather than local detection.
• This is NOT a system configuration issue — all system-level checks confirm Hyper-V is properly installed, running, and functional.

Related Issues

• #25034 — Same bug on Windows 11 Enterprise
• #25136 — yukonSilver unsupported + CoworkVMService cannot be removed
• #27316 — Same bug on Windows 10 Pro
• #27357 — yukonSilver unsupported on Windows 11 Pro (i5-14600K)
• #29532 — Hyper-V alive and well, Claude won't believe it
• #30997 — yukonSilver classified as unsupported on Windows 10 Pro
• #32004 — yukonSilver unsupported despite all features enabled
• #32280 — Same bug on Windows 11 Enterprise
• #32574 — Same bug on Windows 11 Pro