[BUG] Cowork: "yukonSilver not supported" on Windows 11 Pro x64 with Hyper-V fully enabled

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. Claude's workspace requires hardware virtualization (Hyper-V). Enable virtualization in your computer's BIOS/UEFI settings, then restart." — despite all virtualization being fully enabled.
The log file shows the real reason:
yukonSilver not supported (status=unsupported)
The VM is being skipped entirely with VM not supported (win32/x64) repeated constantly in the logs.
System:

Windows 11 Pro x64
Intel VT-x enabled in BIOS
All Hyper-V features enabled and confirmed via PowerShell

Enabled features confirmed:

VirtualMachinePlatform
HypervisorPlatform
Microsoft-Hyper-V-All
Microsoft-Hyper-V
Microsoft-Hyper-V-Hypervisor
Microsoft-Hyper-V-Services

Log location: %LOCALAPPDATA%\Packages\Claude_pzs8sxrjxfjjc\LocalCache\Roaming\Claude\logs\cowork_vm_node.log
Related issues: #25136, #27316

What Should Happen?

Cowork should detect that hardware virtualization is fully enabled, successfully start the VM, and allow access to the Cowork workspace without showing the "Virtualization is not enabled" error. The yukonSilver platform check should either support Windows 11 Pro x64 or provide a meaningful error message explaining why the platform is unsupported.

Error Messages/Logs

2026-02-21 13:03:25 [info] [cleanupVMBundleIfUnsupported] yukonSilver not supported (status=unsupported), checking for stale bundle...
2026-02-21 13:03:27 [warn] [startVM] VM not supported (win32/x64), skipping
2026-02-21 13:03:27 [info] [Callbacks] Initializing VM event callbacks...
2026-02-21 13:03:27 [info] [VM] Loading vmClient (TypeScript) module...
2026-02-21 13:03:27 [info] [VM] Module loaded successfully
2026-02-21 13:03:27 [info] [Callbacks] VM event callbacks initialized
2026-02-21 13:03:29 [warn] [startVM] VM not supported (win32/x64), skipping

UI error message: "Virtualization is not enabled. Claude's workspace requires hardware virtualization (Hyper-V). Enable virtualization in your computer's BIOS/UEFI settings, then restart."

Steps to Reproduce

1- Install latest Claude Desktop on Windows 11 Pro x64
2- Ensure all Hyper-V features are enabled (VirtualMachinePlatform, HypervisorPlatform, Microsoft-Hyper-V-All)
3- Ensure Intel VT-x is enabled in BIOS
4- Open Claude Desktop
5- Navigate to the Cowork tab
6- Observe "Virtualization is not enabled" error message
7- Check log at %LOCALAPPDATA%\Packages\Claude_pzs8sxrjxfjjc\LocalCache\Roaming\Claude\logs\cowork_vm_node.log — shows yukonSilver not 8- supported (status=unsupported) repeatedly

Claude Model

Sonnet (default)

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

2.1.49

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

_No response_