[BUG] [BUG] Cowork yukonSilver classified unsupported on Windows 11 Pro 25H2 Build 26200 — service healthy, renderer detection fails

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?

Summary

Renderer's cleanupVMBundleIfUnsupported returns status=unsupported on Build 26200 despite all platform prerequisites being met. VM bundle never provisioned. Same fingerprint as #27357, #27385, #27445, #29322, #37016 — all still unresolved as of May 2026.

## Environment

• OS: Windows 11 Pro 25H2, Build 26200
• Claude Desktop: 1.8555.2.0 (MSIX, package family Claude_pzs8sxrjxfjjc)
• Install path: C:\Program Files\WindowsApps\Claude_1.8555.2.0_x64__pzs8sxrjxfjjc
• Account: AzureAD-joined corporate device
• Subscription: Pro

## Prerequisites verified

• VirtualizationBasedSecurity: Running
• Microsoft-Hyper-V-All: Enabled
• VirtualMachinePlatform: Enabled
• HypervisorPlatform: Enabled
• HypervisorPresent (Win32_ComputerSystem): True
• vmms service: Running (Automatic)
• vmcompute service: Running (Manual)
• CoworkVMService: Registered, AUTO_START, binary path correct
• AppX volumes: single default C: volume, no redirection
• User AppData: C:\Users\<user>\AppData (on C:)

## Reproduction

1. Open Claude Desktop
2. Click Cowork tab
3. Observe banner: "Cowork requires a newer installation"
4. %APPDATA%\Claude\logs\cowork_vm_node.log writes:

Key observation — service is healthy, renderer check fails

Manually starting CoworkVMService via sc.exe start CoworkVMService succeeds:

• STATE: 4 RUNNING, stable PID
• WIN32_EXIT_CODE: 0
• Service does not crash, does not exit, runs indefinitely

Yet the renderer continues to log yukonSilver not supported on every check. This isolates the defect to the renderer's TypeScript/Node platform-detection path, not to cowork-svc.exe.

## Bundle status
No vm_bundle / yukonSilver directory anywhere on disk — neither under %LOCALAPPDATA%\Claude nor under %LOCALAPPDATA%\Packages\Claude_pzs8sxrjxfjjc\LocalState. Bundle download was never triggered because detection short-circuits beforehand.

## Duration
Reproduces on every launch since 27 April 2026. cowork_vm_node.log contains 30+ consecutive identical entries spanning ~4 weeks.

## Anthropic support reference
Conversation ID 215474420709700 — full logs and diagnostic chain on file with support.

## Request
Fix build-detection logic to recognise Windows 11 25H2 Build 26200 (GA since September 2025) as a supported platform.

What Should Happen?

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

Key observation — service is healthy, renderer check fails

Manually starting CoworkVMService via sc.exe start CoworkVMService succeeds:

• STATE: 4 RUNNING, stable PID
• WIN32_EXIT_CODE: 0
• Service does not crash, does not exit, runs indefinitely

Yet the renderer continues to log yukonSilver not supported on every check. This isolates the defect to the renderer's TypeScript/Node platform-detection path, not to cowork-svc.exe.

## Bundle status
No vm_bundle / yukonSilver directory anywhere on disk — neither under %LOCALAPPDATA%\Claude nor under %LOCALAPPDATA%\Packages\Claude_pzs8sxrjxfjjc\LocalState. Bundle download was never triggered because detection short-circuits beforehand.

## Duration
Reproduces on every launch since 27 April 2026. cowork_vm_node.log contains 30+ consecutive identical entries spanning ~4 weeks.

## Anthropic support reference
Conversation ID 215474420709700 — full logs and diagnostic chain on file with support.

## Request
Fix build-detection logic to recognise Windows 11 25H2 Build 26200 (GA since September 2025) as a supported platform.

Error Messages/Logs

## Key observation — service is healthy, renderer check fails
   Manually starting `CoworkVMService` via `sc.exe start CoworkVMService` succeeds:
   - STATE: 4 RUNNING, stable PID
   - WIN32_EXIT_CODE: 0
   - Service does not crash, does not exit, runs indefinitely

   Yet the renderer continues to log `yukonSilver not supported` on every check. This isolates the defect to the renderer's TypeScript/Node platform-detection path, not to `cowork-svc.exe`.

   ## Bundle status
   No `vm_bundle` / `yukonSilver` directory anywhere on disk — neither under `%LOCALAPPDATA%\Claude` nor under `%LOCALAPPDATA%\Packages\Claude_pzs8sxrjxfjjc\LocalState`. Bundle download was never triggered because detection short-circuits beforehand.

   ## Duration
   Reproduces on every launch since 27 April 2026. `cowork_vm_node.log` contains 30+ consecutive identical entries spanning ~4 weeks.

   ## Anthropic support reference
   Conversation ID 215474420709700 — full logs and diagnostic chain on file with support.

   ## Request
   Fix build-detection logic to recognise Windows 11 25H2 Build 26200 (GA since September 2025) as a supported platform.

Steps to Reproduce

Key observation — service is healthy, renderer check fails

Manually starting CoworkVMService via sc.exe start CoworkVMService succeeds:

• STATE: 4 RUNNING, stable PID
• WIN32_EXIT_CODE: 0
• Service does not crash, does not exit, runs indefinitely

Yet the renderer continues to log yukonSilver not supported on every check. This isolates the defect to the renderer's TypeScript/Node platform-detection path, not to cowork-svc.exe.

## Bundle status
No vm_bundle / yukonSilver directory anywhere on disk — neither under %LOCALAPPDATA%\Claude nor under %LOCALAPPDATA%\Packages\Claude_pzs8sxrjxfjjc\LocalState. Bundle download was never triggered because detection short-circuits beforehand.

## Duration
Reproduces on every launch since 27 April 2026. cowork_vm_node.log contains 30+ consecutive identical entries spanning ~4 weeks.

## Anthropic support reference
Conversation ID 215474420709700 — full logs and diagnostic chain on file with support.

## Request
Fix build-detection logic to recognise Windows 11 25H2 Build 26200 (GA since September 2025) as a supported platform.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

LATEST

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

_No response_