[BUG] Cowork fails to start on Windows — "yukonSilver not supported" despite virtualization enabled and CoworkVMService running

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?

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report
• [x] I am using the latest version of Claude Desktop

What's Wrong?

Cowork workspace fails to start on Windows. The reinstall button in the Cowork tab does nothing. Logs show the VM is repeatedly marked as unsupported (yukonSilver not supported) despite virtualization being fully enabled and CoworkVMService running.

This appears related to #25136, #25205, and #27350.

Error Messages

From %APPDATA%\Claude\logs\cowork_vm_node.log:

[info] [cleanupVMBundleIfUnsupported] yukonSilver not supported (status=unsupported), checking for stale bundle...
[warn] [startVM] VM not supported (win32/x64), skipping
[error] [Callbacks] Swift VM addon not available for callbacks

These messages repeat on every launch attempt. The reinstall button produces no change — the VM is immediately skipped each time.

Steps to Reproduce

1. Open Claude Desktop on Windows
2. Navigate to the Cowork tab
3. Attempt to start a Cowork session — fails immediately
4. Click the "Reinstall" button — nothing happens
5. Restart Claude Desktop — same behavior

Expected Behavior

Cowork workspace should start successfully. The reinstall button should re-provision the VM and resolve the "unsupported" state.

Troubleshooting Already Attempted

• Verified virtualization is enabled: systeminfo confirms "A hypervisor has been detected"
• Confirmed CoworkVMService is installed and running (STATE: 4 RUNNING)
• Restarted Claude Desktop multiple times
• Restarted computer
• Reinstall button in Cowork tab has no effect

Environment

• Claude Desktop version: 1.1.4088 (7e63fd) 2026-02-23T21:25:53.000Z
• OS: Windows (win32/x64)
• Virtualization: Enabled (hypervisor detected)
• CoworkVMService: Installed and running
• Subscription: Team or Enterprise (organization account — SecureAuth Corporation)
• Previously working: No — Cowork has never worked on this machine
• Note: A colleague at the same organization with identical account permissions has Cowork working on macOS. This appears to be a Windows-specific issue.

What Should Happen?

Cowork should work seamlessly on Windows.

Error Messages/Logs

Steps to Reproduce

See What's Wrong section.

Claude Model

None

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

2.0.0 (Claude Code)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

_No response_