[BUG] Cowork: yukonSilver unsupported on Windows 11 Insider Preview 25H2 build 26220 — VM service starts then immediately stops

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 fails to start on Windows 11 Insider Preview 25H2 (build 26220.7934). The log explicitly marks yukonSilver as unsupported (status=unsupported) and skips the VM entirely. The CoworkVMService installs and can be started manually via PowerShell but stops immediately when Claude attempts to initialize it.

What Should Happen?

Cowork VM should start successfully with Hyper-V enabled on Windows 11 Pro.

Error Messages/Logs

yukonSilver not supported (status=unsupported) and VM not supported (win32/x64), skipping. CoworkVMService stops immediately after starting.

Steps to Reproduce

nstall Claude Desktop 1.1.4498 on Windows 11 Insider Preview 25H2 build 26220.7934
Enable Hyper-V (Microsoft-Hyper-V-All and HypervisorPlatform)
Reboot
Open Claude Desktop and navigate to Cowork
Observe error: "Failed to start Claude's workspace — VM service not running"

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

Claude Desktop: 1.1.4498

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

Environment

Claude Desktop: 1.1.4498 (24f768) 2026-02-26
OS: Windows 11 Pro Insider Preview 25H2, build 26220.7934
CPU: AMD Ryzen 7 5800X3D
Hyper-V: Enabled (vmms Running/Automatic)
Subscription: (put your plan here — Max, Pro, etc.)

Related Issues
#27801, #25136