[BUG] Cowork "VM not supported (win32/x64)" on Windows 11 Pro 25H2 Build 26200 — yukonSilver unsupported despite all virtualization 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" error. The cowork_vm_node.log shows yukonSilver not supported (status=unsupported) and repeatedly logs VM not supported (win32/x64), skipping. All virtualization features are enabled and confirmed working — WSL2 runs fine, Hyper-V services are running, CoworkVMService is running.

What Should Happen?

Cowork should detect the fully-enabled virtualization stack and start its VM successfully on Windows 11 Pro 25H2 (Build 26200) with x64 architecture.

Error Messages/Logs

2026-02-21 15:07:36 [info] [cleanupVMBundleIfUnsupported] yukonSilver not supported (status=unsupported), checking for stale bundle...
2026-02-21 15:07:39 [warn] [startVM] VM not supported (win32/x64), skipping
2026-02-21 15:07:39 [info] [Callbacks] Initializing VM event callbacks...
2026-02-21 15:07:39 [info] [VM] Loading vmClient (TypeScript) module...
2026-02-21 15:07:39 [info] [VM] Module loaded successfully
2026-02-21 15:07:39 [info] [Callbacks] VM event callbacks initialized
2026-02-21 15:07:40 [warn] [startVM] VM not supported (win32/x64), skipping

Steps to Reproduce

1. Install Claude Desktop v1.1.3918 (MSIX) on Windows 11 Pro x64 (Build 26200)
2. Ensure all virtualization features are enabled (Hyper-V, VMP, HypervisorPlatform, WSL2)
3. Launch Claude Desktop → navigate to Cowork tab
4. Observe: "Virtualization is not enabled" error

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

N/A — Claude Desktop v1.1.3918 (MSIX package: Claude_1.1.3918.0_x64__pzs8sxrjxfjjc)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

Environment

• OS: Windows 11 Pro, version 25H2 (Build 26200)
• CPU: Intel Core Ultra 9 275HX (24C/24T)
• GPU: NVIDIA RTX 5090 Laptop (24GB VRAM)
• RAM: 64 GB DDR5
• Installed via: ClaudeSetup.exe → MSIX (upgraded from Squirrel on 2026-02-21 02:52)

Virtualization Status (all confirmed working)

systeminfo:
Virtualization-based security: Status: Running
Hyper-V Requirements: A hypervisor has been detected.

PowerShell:
(Get-CimInstance Win32_ComputerSystem).HypervisorPresent → True

Services:
vmcompute Running Manual
vmms Running Automatic
CoworkVMService Running (TYPE: WIN32_PACKAGED_PROCESS)

WSL2: Ubuntu running (Version 2 confirmed via wsl -l -v)

Claude Desktop Config (claude_desktop_config.json)

{
"mcpServers": { "PowerShell": { ... } },
"preferences": {
"coworkScheduledTasksEnabled": false,
"sidebarMode": "chat"
}
}

Setup Log (ClaudeSetup.log)

2026/02/21 02:52:45 Terminated 10 Squirrel Claude process(es)
2026/02/21 02:52:45 Installing MSIX: Claude-3293026219.msix
2026/02/21 02:52:48 MSIX package installed successfully
2026/02/21 02:52:49 Squirrel installation removed
2026/02/21 02:52:49 === Claude Setup completed successfully ===

Attempted Fixes (none resolved)

• Full PC reboot after Hyper-V enablement
• Closed Claude Desktop completely from system tray → reopened
• Verified CoworkVMService is running
• Verified all features: Microsoft-Hyper-V-All + HypervisorPlatform + VirtualMachinePlatform

Related Issues

• #27330 — Same "VM not supported (win32/x64)" on Win10 Pro
• #27316 — Same "Virtualization not enabled" despite Hyper-V on Win10 Pro
• #25136 — yukonSilver marked unsupported on Build 26200
• #25914 — CoworkVMService crashes on Build 26200

Suspected Root Cause

The yukonSilver platform detection module incorrectly classifies win32/x64 on Windows 11 Pro Build 26200 as unsupported, even when all virtualization infrastructure is fully operational.