[BUG] Cowork "yukonSilver not supported" persists on Windows 11 Pro x64 Build 26200 — issue #25136 closed but not fixed

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 tab shows "Virtualization is not enabled" on Windows 11 Pro x64 Build 26200 despite all virtualization features being fully enabled. The log repeatedly shows yukonSilver not supported (status=unsupported) and the VM never starts.

Issue #25136 was closed as resolved, but the problem persists on this system with the latest version of Claude Desktop (confirmed via Help > Check for Updates — "You are running the most recent version").

sc query CoworkVMService returns nothing — the service was never created after clean reinstall.

What Should Happen?

Expected Behavior

Cowork should start successfully. Issue #25136 was marked as resolved but the fix did not reach this configuration.

Related Issues

#25136 #25142 #25692 #27350

Error Messages/Logs

From `%APPDATA%\Claude\logs\cowork_vm_node.log`:
[warn] [startVM] VM not supported (win32/x64), skipping
[info] [cleanupVMBundleIfUnsupported] yukonSilver not supported (status=unsupported), checking for stale bundle...

Steps to Reproduce

Issue #25136 was closed, but the problem persists on my system with the latest version of Claude Desktop. The Cowork tab shows "Virtualization is not enabled" and the log repeatedly shows yukonSilver not supported (status=unsupported).

Environment

| Component | Details |
|-----------|---------|
| OS | Windows 11 Pro, Build 26200.7840 (25H2) |
| Architecture | x64 |
| CPU | Intel Core i7-1360P (13th Gen) |
| RAM | 16GB |
| Claude Desktop | Latest version (confirmed via Help > Check for Updates — "You are running the most recent version") |
| Plan | Pro |

Confirmed Enabled

• ✅ Intel VT-x (BIOS)
• ✅ Hyper-V (Microsoft-Hyper-V): Enabled
• ✅ Virtual Machine Platform: Enabled
• ✅ Windows Sandbox (Containers-DisposableClientVM): Enabled
• ✅ Virtualization shown as "Enabled" in Task Manager
• ✅ bcdedit /set hypervisorlaunchtype auto executed successfully
• ✅ Full clean reinstall performed (deleted %APPDATA%\Claude and %LOCALAPPDATA%\Claude)

1. Install latest Claude Desktop on Windows 11 Pro x64 Build 26200
2. Enable all virtualization features (Hyper-V, VMP, Windows Sandbox)
3. Open Claude Desktop → Cowork tab
4. Observe: "Virtualization is not enabled" error
5. Check log: yukonSilver not supported (status=unsupported)

Claude Model

Sonnet (default)

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

1.1.3918 (a4b368)

Platform

Other

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

Issue #25136 was closed but the fix did not reach this configuration.
Latest Claude Desktop confirmed via Help > Check for Updates ("You are running the most recent version").

Logs from %APPDATA%\Claude\logs\cowork_vm_node.log:
[warn] [startVM] VM not supported (win32/x64), skipping
[info] [cleanupVMBundleIfUnsupported] yukonSilver not supported (status=unsupported)

All virtualization confirmed enabled:

• Hyper-V: Enabled
• Virtual Machine Platform: Enabled
• Windows Sandbox (Containers-DisposableClientVM): Enabled
• VT-x in BIOS: Enabled
• Task Manager shows Virtualization: Enabled
• bcdedit /set hypervisorlaunchtype auto: executed successfully
• Full clean reinstall performed (deleted %APPDATA%\Claude and %LOCALAPPDATA%\Claude)
• sc query CoworkVMService returns nothing — service was never created

Hardware: Samsung PC, Intel Core i7-1360P (13th Gen), 16GB RAM
OS: Windows 11 Pro, Build 26200.7840 (25H2)

Related: #25136 #25142 #25692 #27350