[BUG] Cowork "yukonSilver unsupported" on Windows 11 Pro ARM64 — MSIX arm64 package, all prerequisites met

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?

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report
• [x] I am using the latest version of Claude Code

What's Wrong?

Cowork tab shows "Cowork requires a newer installation" on Windows 11 Pro ARM64. The Reinstall button does nothing. The VM never attempts to start — yukonSilver is classified as "unsupported" despite all prerequisites being met.

This appears to be a platform detection gap: Anthropic publishes a dedicated ARM64 MSIX package on claude.ai/download, but the yukonSilver VM check rejects ARM64 as unsupported.

Environment

| Property | Value |
|---|---|
| OS | Windows 11 Pro 25H2 (Build 26200.7840) ARM64 |
| Claude Desktop | v1.1.8629.0 (MSIX, arm64) |
| Package | Claude_1.1.8629.0_arm64__pzs8sxrjxfjjc |
| VirtualMachinePlatform | Enabled |
| CoworkVMService | Running |
| Subscription | Pro |

Log output

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

2026-03-26 00:18:22 [info] [cleanupVMBundleIfUnsupported] yukonSilver not supported (status=unsupported), checking for stale bundle...
2026-03-26 00:21:06 [info] [cleanupVMBundleIfUnsupported] yukonSilver not supported (status=unsupported), checking for stale bundle...
2026-03-26 00:29:08 [info] [cleanupVMBundleIfUnsupported] yukonSilver not supported (status=unsupported), checking for stale bundle...

This pattern repeats on every launch since March 10, 2026. The VM never progresses past this check.

Expected Behavior

Cowork should detect ARM64 as a supported platform and start the VM workspace, since Anthropic explicitly offers an ARM64 MSIX package on the download page.

Steps to Reproduce

1. Install Claude Desktop ARM64 MSIX from claude.ai/download
2. Enable VirtualMachinePlatform, reboot
3. Open Claude Desktop → Cowork tab
4. Observe "Cowork requires a newer installation" banner
5. Click Reinstall — nothing happens
6. Check cowork_vm_node.log — "yukonSilver not supported"

Related Issues

• #25136 (yukonSilver unsupported on x64)
• #32004 (same, different build)
• #28238 (same, Build 26200)
• #28998 (Reinstall button does nothing)

None of the above report the ARM64 case specifically.

What Should Happen?

Cowork should detect ARM64 as a supported platform and start the VM workspace, since Anthropic explicitly offers an ARM64 MSIX package on the download page.

Error Messages/Logs

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

2026-03-26 00:18:22 [info] [cleanupVMBundleIfUnsupported] yukonSilver not supported (status=unsupported), checking for stale bundle...
2026-03-26 00:21:06 [info] [cleanupVMBundleIfUnsupported] yukonSilver not supported (status=unsupported), checking for stale bundle...
2026-03-26 00:29:08 [info] [cleanupVMBundleIfUnsupported] yukonSilver not supported (status=unsupported), checking for stale bundle...

This pattern repeats on every launch since March 10, 2026. The VM never progresses past this check.

Steps to Reproduce

1. Install Claude Desktop ARM64 MSIX from claude.ai/download
2. Enable VirtualMachinePlatform, reboot
3. Open Claude Desktop → Cowork tab
4. Observe "Cowork requires a newer installation" banner
5. Click Reinstall — nothing happens
6. Check cowork_vm_node.log — "yukonSilver not supported"

Claude Model

None

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

Claude Desktop v1.1.8629.0 (MSIX arm64)

Platform

Other

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

Related issues: #25136, #32004, #28238, #28998
None of the above report the ARM64 case specifically.