Cowork VM fails to build bundle on Windows 11 Home — VM service stops, bundle empty (rootfs.vhdx/sessiondata.vhdx missing)

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?

aCowork fails with "Failed to start Claude's workspace — VM service not running. The service failed to start."

CoworkVMService is configured as Automatic but stops immediately on launch. The claudevm.bundle directory is created but all VM artifacts are missing:

• rootfs.vhdx = False
• - sessiondata.vhdx = False
• - - vmlinuz = False
• - - - initrd = False

The VM never boots because there is nothing to boot. This has persisted for 6+ days across multiple full reinstalls and reboots.

Environment:

• OS: Windows 11 Home (Core), Build 26200, x64
• - Claude Desktop: v1.1.4498.0 (MSIX / Microsoft Store install)
• - - CoworkVMService binary: C:\Program Files\WindowsApps\Claude_...\cowork-svc.exe
• - - - Claude Code CLI: 2.1.63
• - - - - Hyper-V features: enabled
• - - - - - HNS networks present: "cowork" network exists
• - - - - - - vmcompute, hns, winnat services: running

Key observations:

1. Bundle directory is created but contains zero VM disk files — no rootfs.vhdx, no sessiondata.vhdx, no vmlinuz, no initrd.
2. 2. Networking stack is NOT the issue — HNS service running, "cowork" network exists, no 0x80070032 errors, API reachable.
3. 3. A second Windows 11 Home machine with the same OS edition, same Claude version, and same MSIX install type works correctly and has a fully materialized claudevm.bundle (all four files present).

Actions already attempted:

• Uninstalled and reinstalled Claude Desktop
• - Rebooted multiple times
• - - Verified Hyper-V features
• - - - Verified HNS/WinNAT services
• - - - - Deleted and recreated %APPDATA%\Claude\vm_bundles and %LOCALAPPDATA%\Claude\vm_bundles
• - - - - - Reset TEMP/TMP to system defaults
• - - - - - - Performed full side-by-side diagnostic comparison between working and broken machines
• - - - - - - - Confirmed bundle never builds across all attempts

Hypothesis: This appears to be a bundle materialization failure in the Windows MSIX environment. Possible causes: a file copy/rename failure during bundle assembly, a permission issue inside LocalCache\RoamingState, or a cross-volume rename condition (EXDEV). Logs do not show EXDEV currently — the bundle simply never gets created. The failure occurs before VM boot.

What Should Happen?

aOn first Cowork launch:

1. claudevm.bundle should be created with all required artifacts (rootfs.vhdx, sessiondata.vhdx, vmlinuz, initrd)
2. 2. CoworkVMService should remain running
3. 3. VM should boot successfully

If bundle creation fails, Claude Desktop should:

• Surface the real file error (copy/rename/permission failure)
• - Indicate which specific path failed
• - - Offer a "Rebuild workspace bundle" option
• - - - Avoid generic "VM service not running" messaging that obscures the actual root cause

Error Messages/Logs

aUI Error: "Failed to start Claude's workspace — VM service not running. The service failed to start."

Bundle state on broken machine:
  claudevm.bundle directory: EXISTS (empty)
  rootfs.vhdx:      False
  sessiondata.vhdx: False
  vmlinuz:          False
  initrd:           False

Bundle state on working machine (same OS/version):
  claudevm.bundle directory: EXISTS
  rootfs.vhdx:      True
  sessiondata.vhdx: True
  vmlinuz:          True
  initrd:           True

Note: No EXDEV errors observed in current logs. Bundle simply never gets written.
Diagnostics JSON and cowork_vm_node.log attached.

Steps to Reproduce

a1. Install Claude Desktop via Microsoft Store (MSIX) on Windows 11 Home (Core), Build 26200

1. Install Claude Code CLI 2.1.63
2. 3. Verify Hyper-V features are enabled and HNS/WinNAT/vmcompute services are running
3. 4. Launch Claude Desktop and attempt to start Cowork / Claude's workspace
4. 5. Observe: UI shows "Failed to start Claude's workspace — VM service not running"
5. 6. Check: %APPDATA%\Claude\vm_bundles\claudevm.bundle — directory exists but is empty (no rootfs.vhdx, no sessiondata.vhdx, no vmlinuz, no initrd)
6. 7. CoworkVMService stops immediately; does not remain running

Reproduced 100% consistently. Persists after:

• Full uninstall + reinstall of Claude Desktop
• - Multiple reboots
• - - Deleting and recreating the vm_bundles directory

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.63

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

Engineering Addendum:

I performed a side-by-side structured diagnostic comparison between a working and broken machine. The only material difference is that the working machine successfully builds claudevm.bundle, while the broken machine never writes the VM artifacts. Networking stack and service configuration are equivalent. This suggests the failure occurs during bundle creation, not VM boot.

Attachments (to be added):

• broken-cowork-diag.json
• - broken-cowork-diag.txt
• - - cowork_vm_node.log

Claude Desktop install path: C:\Program Files\WindowsApps\Claude_...\cowork-svc.exe (MSIX / WindowsApps install)

Impact: Cowork is completely unusable on this machine. This has persisted for 6+ days despite full reinstall and system validation.