[BUG] Cowork regression on Windows — yukonSilver marked unsupported after update to v1.1.3918 (was working on previous version)

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?

This is a confirmed regression. Cowork was fully working on my machine until Claude Desktop auto-updated to v1.1.3918.0. After the update, the Cowork tab shows "Virtualization is not enabled" and the VM never boots.

All Hyper-V services are running. The system is identical to when Cowork worked. Nothing changed on my end — only the Claude Desktop version.

The log shows the same yukonSilver not supported pattern reported in #25136, #25142, #25205, #25692 — all closed without a working fix for this configuration.

Environment:

| Component | Details |
|---|---|
| OS | Windows 11 Pro 24H2 |
| Architecture | x64 (Intel i7-14700F) |
| GPU | NVIDIA RTX 4060 Ti |
| Claude Desktop | v1.1.3918.0 |
| Plan | Pro |
| Hyper-V | ✅ Enabled and running |
| vmcompute | ✅ Running |
| vmms | ✅ Running (Automatic) |
| CoworkVMService | ✅ Running (Automatic) |

Verified via systeminfo: hypervisor detected. All three services (vmcompute, vmms, CoworkVMService) confirmed running. The platform detection logic is incorrectly marking a fully functional and previously working system as unsupported.

What Should Happen?

Cowork should work as it did on the previous Claude Desktop version. The VM should boot and the Cowork tab should be functional.

Error Messages/Logs

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

2026-02-21 04:51:17 [info] [cleanupVMBundleIfUnsupported] yukonSilver not supported (status=unsupported), checking for stale bundle...
2026-02-21 04:51:17 [info] [deleteVMBundle] Deleting reinstall files from C:\Users\...\Claude\vm_bundles\claudevm.bundle
2026-02-21 04:51:17 [info] [deleteVMBundle] Reinstall files deleted (sessiondata.img and rootfs.img.zst preserved)
2026-02-21 04:51:20 [warn] [startVM] VM not supported (win32/x64), skipping
2026-02-21 04:51:20 [info] [Callbacks] Initializing VM event callbacks...
2026-02-21 04:51:20 [info] [VM] Loading vmClient (TypeScript) module...
2026-02-21 04:51:20 [info] [VM] Module loaded successfully
2026-02-21 04:51:20 [info] [Callbacks] VM event callbacks initialized
2026-02-21 04:51:22 [warn] [startVM] VM not supported (win32/x64), skipping

This pattern repeats indefinitely. The VM never attempts to boot.

Services confirmed running (PowerShell output):

vmcompute      Running    Manual
vmms           Running    Automatic
CoworkVMService Running   Automatic

Steps to Reproduce

1. Have a working Cowork installation on Windows 11 Pro x64 with Hyper-V
2. Allow Claude Desktop to auto-update to v1.1.3918.0
3. Cowork stops working — shows "Virtualization is not enabled"
4. Log shows yukonSilver not supported (status=unsupported) and VM not supported (win32/x64), skipping

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

The version immediately before 1.1.3918 (exact number unknown — auto-update)

Claude Code Version

1.1.3918

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

Related closed issues (same root cause, none resolved): #25136, #25142, #25205, #25692