[BUG] Cowork regression on Windows — yukonSilver marked unsupported after update to v1.1.3918 (was working on previous version)
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?
This is a confirmed regression. Cowork was fully working on my machine until Claude Desktop auto-updated to v1.1.3918.0. After the update, the Cowork tab shows "Virtualization is not enabled" and the VM never boots.
All Hyper-V services are running. The system is identical to when Cowork worked. Nothing changed on my end — only the Claude Desktop version.
The log shows the same yukonSilver not supported pattern reported in #25136, #25142, #25205, #25692 — all closed without a working fix for this configuration.
Environment:
| Component | Details |
|---|---|
| OS | Windows 11 Pro 24H2 |
| Architecture | x64 (Intel i7-14700F) |
| GPU | NVIDIA RTX 4060 Ti |
| Claude Desktop | v1.1.3918.0 |
| Plan | Pro |
| Hyper-V | ✅ Enabled and running |
| vmcompute | ✅ Running |
| vmms | ✅ Running (Automatic) |
| CoworkVMService | ✅ Running (Automatic) |
Verified via systeminfo: hypervisor detected. All three services (vmcompute, vmms, CoworkVMService) confirmed running. The platform detection logic is incorrectly marking a fully functional and previously working system as unsupported.
What Should Happen?
Cowork should work as it did on the previous Claude Desktop version. The VM should boot and the Cowork tab should be functional.
Error Messages/Logs
From %APPDATA%\Claude\logs\cowork_vm_node.log:
2026-02-21 04:51:17 [info] [cleanupVMBundleIfUnsupported] yukonSilver not supported (status=unsupported), checking for stale bundle...
2026-02-21 04:51:17 [info] [deleteVMBundle] Deleting reinstall files from C:\Users\...\Claude\vm_bundles\claudevm.bundle
2026-02-21 04:51:17 [info] [deleteVMBundle] Reinstall files deleted (sessiondata.img and rootfs.img.zst preserved)
2026-02-21 04:51:20 [warn] [startVM] VM not supported (win32/x64), skipping
2026-02-21 04:51:20 [info] [Callbacks] Initializing VM event callbacks...
2026-02-21 04:51:20 [info] [VM] Loading vmClient (TypeScript) module...
2026-02-21 04:51:20 [info] [VM] Module loaded successfully
2026-02-21 04:51:20 [info] [Callbacks] VM event callbacks initialized
2026-02-21 04:51:22 [warn] [startVM] VM not supported (win32/x64), skipping
This pattern repeats indefinitely. The VM never attempts to boot.
Services confirmed running (PowerShell output):
vmcompute Running Manual
vmms Running Automatic
CoworkVMService Running AutomaticSteps to Reproduce
- Have a working Cowork installation on Windows 11 Pro x64 with Hyper-V
- Allow Claude Desktop to auto-update to v1.1.3918.0
- Cowork stops working — shows "Virtualization is not enabled"
- Log shows yukonSilver not supported (status=unsupported) and VM not supported (win32/x64), skipping
Claude Model
Opus
Is this a regression?
Yes, this worked in a previous version
Last Working Version
The version immediately before 1.1.3918 (exact number unknown — auto-update)
Claude Code Version
1.1.3918
Platform
Anthropic API
Operating System
Windows
Terminal/Shell
PowerShell
Additional Information
Related closed issues (same root cause, none resolved): #25136, #25142, #25205, #25692
5 Comments
Found 3 possible duplicate issues:
This issue will be automatically closed as a duplicate in 3 days.
🤖 Generated with Claude Code
This is NOT a duplicate. The referenced issues are either closed without resolution or describe different scenarios (fresh installs, different OS versions).
This issue is a confirmed regression: Cowork was working on this exact machine with Hyper-V enabled and all services running. The only change was the Claude Desktop auto-update to v1.1.3918.0.
The previous issues (#25136, #25142, #25692) were all closed — none resulted in a fix. Closing this as a duplicate of already-closed issues means the bug is never tracked as open.
If there IS an active tracking issue for this problem, please link it instead of auto-closing.
Cowork was working fine yesterday, but after the auto-update it stopped working.
Now it shows the error: "Virtualization is not enabled. Claude's workspace requires hardware virtualization (Hyper-V)."
However, all virtualization settings are properly configured:
Hyper-V: ✅ Enabled
Windows Hypervisor Platform: ✅ Enabled
bcdedit hypervisorlaunchtype: Auto
Hyper-V services: Running
OS: Windows 11 Pro 25H2 (Build 26200)
Claude version: 1.1.3918
This appears to be a regression introduced in a recent update. Please fix this.
Thanks for confirming. This issue is closed — please add your report to #25034, that's where the bug is being tracked.
This issue has been automatically locked since it was closed and has not had any activity for 7 days. If you're experiencing a similar issue, please file a new issue and reference this one if it's relevant.