[BUG] Cowork "Virtualization is not enabled" after update — yukonSilver marked unsupported on win32/x64

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?

a## Environment

• OS: Windows 11 Pro (Build 26200)
• - CPU: AMD Ryzen 7 7800X3D
• - - RAM: 64 GB
• - - - GPU: NVIDIA RTX 4090
• - - - - Claude Desktop: Latest version (as of 2026-02-21)

Description

Cowork was working fine earlier today (07:42 UTC). After Claude Desktop updated/restarted, the Cowork tab now shows "Virtualization is not enabled" and blocks all input.

However, Hyper-V is fully functional:

• HyperVisorPresent: True
• - vmcompute service: Running
• - - vmms service: Running (StartType: Automatic)
• - - - CoworkVMService: Running (StartType: Automatic)
• - - - - WslService: Running
• - - - - - VirtualizationBasedSecurityStatus: 2 (Running)

Root Cause (from logs)

The cowork_vm_node.log reveals the issue clearly:

Before the break (07:42 UTC) — VM working normally:

[Spawn:vm] Spawn succeeded in 2460ms
[startVM] VM already connected

After the break (17:27 UTC) — VM marked as unsupported:

[cleanupVMBundleIfUnsupported] yukonSilver not supported (status=unsupported), checking for stale bundle...
[deleteVMBundle] Deleting reinstall files from ...\vm_bundles\claudevm.bundle
[startVM] VM not supported (win32/x64), skipping

The yukonSilver VM bundle was marked as unsupported, which triggered automatic deletion of the VM files. From that point on, every attempt to start the VM fails with VM not supported (win32/x64), skipping — repeated dozens of times in the logs.

Key Evidence

1. The VM bundle directory is empty — vm_bundles and claude-code-vm contain no .vhdx files
2. 2. Hyper-V works perfectly — all services running, hypervisor detected
3. 3. The error message is misleading — it says "Enable virtualization in your BIOS" but the real issue is the VM bundle being flagged as unsupported
4. 4. This appears to be related to issues #27316 and #27350
5. ## Expected Behavior

Cowork should either:

• Continue supporting the yukonSilver bundle on Windows x64, or
• - Automatically download and provision an updated/compatible VM bundle

Steps to Reproduce

1. Have a working Cowork installation on Windows 11 x64
2. 2. Update Claude Desktop (or wait for server-side config change)
3. 3. Open Cowork tab → "Virtualization is not enabled" error
4. 4. Check cowork_vm_node.log → yukonSilver not supported (status=unsupported)

What Should Happen?

aCowork should detect the working Hyper-V environment and either continue using the existing VM bundle or automatically download and provision a compatible replacement. The error message should accurately describe the issue (VM bundle incompatibility) rather than incorrectly telling the user to enable BIOS virtualization.

Error Messages/Logs

a2026-02-21 17:27:25 [info] [cleanupVMBundleIfUnsupported] yukonSilver not supported (status=unsupported), checking for stale bundle...
2026-02-21 17:27:25 [info] [deleteVMBundle] Deleting reinstall files from C:\Users\<user>\AppData\Roaming\Claude\vm_bundles\claudevm.bundle
2026-02-21 17:27:25 [info] [deleteVMBundle] Reinstall files deleted (sessiondata.img and rootfs.img.zst preserved)
2026-02-21 17:28:40 [warn] [startVM] VM not supported (win32/x64), skipping
2026-02-21 17:28:41 [warn] [startVM] VM not supported (win32/x64), skipping
2026-02-21 17:28:44 [warn] [startVM] VM not supported (win32/x64), skipping
... (repeats dozens of times)

Steps to Reproduce

1. Have a working Cowork installation on Windows 11 x64 (was working earlier today at 07:42 UTC)
2. At some point, an update or server-side config change marked yukonSilver VM bundle as unsupported
3. Open Claude Desktop → navigate to Cowork tab
4. Observe "Virtualization is not enabled" error message
5. Check cowork_vm_node.log → [cleanupVMBundleIfUnsupported] yukonSilver not supported (status=unsupported)
6. VM files are automatically deleted and every subsequent VM start attempt fails with [startVM] VM not supported (win32/x64), skipping

Note: Hyper-V is fully functional — vmcompute and vmms services running, HyperVisorPresent = True, VBS status = 2 (running). The issue is purely that the yukonSilver bundle was flagged as unsupported.

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

Claude Desktop 1.1.3918 (Windows Store / MSIX)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

_No response_