[BUG] Cowork "yukonSilver not supported" on Windows 11 25H2 (Build 26200) — stable GA channel

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?

The Cowork tab shows "Cowork requires a newer installation" and the Reinstall button does nothing. The VM never starts.

Related to #28238 (closed as duplicate/stale) and #25136. Filing fresh to confirm this persists on the STABLE 25H2 GA release (Build 26200), not Insider/Dev.

Environment:

• OS: Windows 11 25H2, Build 26200.0 — General Availability / stable channel, NOT Insider
• CPU: AMD Ryzen 7 8700F (x64)
• App: Claude Desktop 1.12603.1, installed via winget (Anthropic.Claude), installer hash verified
• Plan: Max (individual account)

Already verified / ruled out:

• VirtualizationFirmwareEnabled => True
• VirtualMachinePlatform feature enabled + rebooted
• vmcompute service Running, StartType Automatic
• Clean reinstall: uninstall + deleted %LOCALAPPDATA%\AnthropicClaude and %APPDATA%\Claude, then fresh install
• Build is >= 19041 per the documented platform check, yet yukonSilver is still flagged unsupported

Build 26200 (25H2) is now a stable GA release, so this affects regular users, not just Insider builds.

What Should Happen?

The yukonSilver VM should recognize Windows 11 Build 26200 (25H2) as a supported platform, since Hyper-V and all required virtualization features are enabled. Cowork should initialize and the tab should be functional. Request: add Build 26200 to the yukonSilver supported-build list.

Error Messages/Logs

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

[cleanupVMBundleIfUnsupported] yukonSilver not supported (status=unsupported), checking for stale bundle...

Steps to Reproduce

1. Install Claude Desktop on Windows 11 25H2 (Build 26200) via winget (Anthropic.Claude)
2. Enable VirtualMachinePlatform and reboot; confirm vmcompute service is Running
3. Open Claude Desktop and click the Cowork tab
4. Result: "Cowork requires a newer installation" appears; Reinstall button does nothing; VM never starts
5. Log %APPDATA%\Claude\logs\cowork_vm_node.log shows: yukonSilver not supported (status=unsupported)

Note: This is the Cowork desktop feature, not the Claude Code CLI. Reproducible on any Windows 11 Build 26200 (25H2) machine with virtualization fully enabled.

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

Claude Desktop 1.12603.1 (Cowork desktop, not Claude Code CLI)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

Environment verified:

• VirtualizationFirmwareEnabled => True
• VirtualMachinePlatform enabled + rebooted
• vmcompute service Running, StartType Automatic
• Clean reinstall performed (deleted %LOCALAPPDATA%\AnthropicClaude and %APPDATA%\Claude)
• Build 26200 is >= 19041 per documented platform check, yet yukonSilver is flagged unsupported

Related: #28238 (closed as duplicate/stale), #25136

Request: add Build 26200 (Windows 11 25H2 GA) to the yukonSilver supported-build list.