[BUG] Cowork: yukonSilver not supported on Windows 11 Pro Build 26200

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 never appears. The app shows "reinstall to use Cowork"
but reinstalling does not fix it.

Environment

• OS: Windows 11 Pro, Build 26200 (stable 25H2, no Insider enrollment)
• App version: 1.1.6452 (Squirrel install)
• Arch: x64

What I checked

• All local files present: cowork-svc.exe (10.6 MB), smol-bin.x64.vhdx (36 MB)
• WindowsSelfHost registry keys: BranchName, Ring, ContentType all empty
• Subscription: Pro

What Should Happen?

Expected behavior
Cowork tab should appear and VM should start.

Error Messages/Logs

**Log entry (cowork_vm_node.log)**
  [cleanupVMBundleIfUnsupported] yukonSilver not supported (status=unsupported)
  [warn] [startVM] VM not supported (win32/x64), skipping

Steps to Reproduce

1. Install Claude Desktop App (Squirrel installer, version 1.1.6452)
2. Open the app
3. Cowork tab is visible but grayed out / disabled
4. Banner shows: "Reinstall Claude Desktop App to use Cowork"
5. Reinstall the app → same result, Cowork tab still grayed out

Claude Model

Sonnet (default)

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

2.1.74

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Other

Additional Information

_No response_