[BUG] Cowork Windows — Plan9 mount fails persistently across multiple workarounds (Win 11 Pro, Max plan)

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?

[BUG] Cowork Windows — Plan9 mount fails persistently across multiple workarounds (Win 11 Pro, Max plan)

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?

Cowork on Windows 11 Pro fails persistently with RPC error -1: failed to ensure virtiofs mount: Plan9 mount failed: bad address. This error has survived every documented workaround over a multi-hour troubleshooting session. The root cause appears to be that the Plan9/virtiofs layer cannot mount directories under a user profile path that contains spaces and/or hyphens.

I am a Max plan subscriber who upgraded specifically for Cowork. After an extended troubleshooting session (approximately 4 hours), Cowork remains non-functional on my system.

Environment

• OS: Windows 11 Pro
• Hyper-V: Enabled (confirmed via Get-WindowsOptionalFeature)
• HypervisorPlatform: Enabled
• VirtualMachinePlatform: Enabled
• Claude Desktop: Latest version (auto-updated March 7, 2026)
• Subscription: Max plan
• User profile path: C:\Users\Chris Duncanson-Hale (contains space and hyphen)

Errors Encountered (in sequence)

Over the course of troubleshooting, the following errors appeared in this order:

1. RPC error -1: process with name "stoic-kind-meitner" already running — orphaned process from prior session
2. VM service not running. The service failed to start. — CoworkVMService stopped, NAT rule missing
3. RPC error -1: failed to ensure virtiofs mount: Plan9 mount failed: bad address — persistent, survived all workarounds
4. Request timed out — workspace failed to initialise
5. RPC error -1: failed to ensure virtiofs mount: Plan9 mount failed: bad address — recurred after reboot and update

Workarounds Attempted (All Failed)

1. Orphaned process cleanup

Killed all Claude/Cowork processes via Get-Process -Name "*claude*","*cowork*" | Stop-Process -Force. Result: Cleared error #1, progressed to error #2.

2. Manual NAT rule creation

Get-NetNat and Get-HnsNetwork both returned empty — no NAT infrastructure existed. Manually created:

New-NetNat -Name "cowork-vm-nat" -InternalIPInterfaceAddressPrefix "172.16.0.0/24"

NAT rule created successfully (Active: True, Store: Local). CoworkVMService started successfully after this. Result: Fixed error #2. Progressed to error #3 (Plan9 mount).

Note: NAT rule does not persist across reboots (Store: Local). Must be manually recreated every restart.

3. VM cache clear and rebuild

Remove-Item -Recurse -Force "$env:APPDATA\Claude\claude-code-vm"
Remove-Item -Recurse -Force "$env:APPDATA\Claude\vm_bundles"

Allowed full VM rebuild. All bundle files downloaded successfully (rootfs.vhdx, sessiondata.vhdx, vmlinuz, initrd, smol-bin.vhdx confirmed present). Result: Plan9 error persisted.

4. Workspace folder moved off OneDrive

Original path was C:\Users\Chris Duncanson-Hale\OneDrive\Desktop\Drive-Cleanup. Moved to C:\Users\Chris Duncanson-Hale\Drive-Cleanup (local, not cloud-synced). Result: Plan9 error persisted.

5. NTFS junction to bypass spaces in path

Created junction: New-Item -ItemType Junction -Path "C:\ClaudeWork" -Target "$env:USERPROFILE". Windows Explorer could read files through the junction. Result: Cowork folder picker accepted the path, but the VM could not see any files through the junction (workspace appeared empty). Junctions are not followed by the VM's filesystem mount.

6. 8.3 short name path

Discovered short name via dir /x: CHRISD~1 maps to Chris Duncanson-Hale. Attempted to use C:\Users\CHRISD~1\Drive-Cleanup. Result: Cowork's folder picker is a GUI dialog with no address bar or text input field — cannot type or paste a path. Can only click through folder tree, which resolves to the long name.

7. Separate Windows user account (theol)

Used an existing local admin account theol (profile path: C:\Users\theol.DESKTOP-5896J6M — no spaces). Copied workspace files there. Granted theol filesystem access to primary user's directories via icacls. Result: Cowork initialised and began running, but could not access the primary user's files at C:\Users\Chris Duncanson-Hale despite admin permissions and explicit icacls grant. Plan9 mount error recurred after reboot (NAT rule lost).

8. Claude Desktop update

Updated to latest version (auto-update on March 7, 2026). Full quit, relaunch, re-created NAT rule. Result: Plan9 error persisted on primary account.

Steps to Reproduce

1. Have a Windows user profile with spaces or hyphens in the path (e.g., C:\Users\Chris Duncanson-Hale)
2. Install Claude Desktop, subscribe to Max plan
3. Enable Hyper-V, HypervisorPlatform, VirtualMachinePlatform
4. Manually create NAT rule (since it is not auto-created): New-NetNat -Name "cowork-vm-nat" -InternalIPInterfaceAddressPrefix "172.16.0.0/24"
5. Start CoworkVMService: net start CoworkVMService
6. Open Claude Desktop → Cowork tab
7. Select any folder under the user profile
8. Observe: RPC error -1: failed to ensure virtiofs mount: Plan9 mount failed: bad address

Expected Behaviour

Cowork should:

• Auto-create the NAT rule on startup (and persist it across reboots)
• Successfully mount directories under user profile paths that contain spaces and hyphens (this is extremely common on Windows — any user with a multi-word name will have this)
• Provide a text input field in the folder picker so users can paste paths (including 8.3 short names)

Actual Behaviour

• NAT rule is never auto-created; must be manually created via PowerShell every reboot
• Plan9/virtiofs mount fails on any path containing spaces or hyphens
• Folder picker has no text input, making workaround paths inaccessible
• The combination of these three issues makes Cowork completely unusable for any Windows user whose profile name contains a space

Impact

This is not a configuration issue — it is a fundamental compatibility gap with standard Windows user profiles. Any Windows user who set up their account with their full name (the default behaviour during Windows setup) will have spaces in their profile path. This likely affects a large percentage of Windows users.

I am a paying Max subscriber who upgraded specifically for Cowork functionality. After 4+ hours of troubleshooting with detailed technical knowledge, Cowork remains non-functional. A non-technical user would have no path to resolution.

Related Issues

• #26554 — Plan9 mount failed: bad address (Windows 11 Pro)
• #29587 — virtiofs/Plan9 mount fails after brief use
• #25419 — sandbox-helper fails to unmount host share, VM service won't start
• #25235 — Downloads folder fails to mount
• #25293 — sandbox-helper fails with OneDrive-synced folders
• #29848 — Cowork completely unusable, rotating errors including Plan9
• #25155 — VM boots but cannot reach API, NAT rule not created
• #27576 — virtiofs mount failure after ~1 hour of use
• #25206 — VM starts but crashes within 5 minutes
• #24945 — VM boots but API unreachable
• #27801 — VM service not running, persists after reboot

System Details

WindowsEditionId: Professional
Hyper-V: Enabled
HypervisorPlatform: Enabled
VirtualMachinePlatform: Enabled
CoworkVMService: Starts successfully (after manual NAT creation)
User profile: C:\Users\Chris Duncanson-Hale
VM bundle: All files present and checksums valid
NAT rule: Must be manually created; Store: Local (does not persist)

What Should Happen?

Cowork should:

• Auto-create the NAT rule on startup (and persist it across reboots)
• Successfully mount directories under user profile paths that contain spaces and hyphens (this is extremely common on Windows — any user with a multi-word name will have this)
• Provide a text input field in the folder picker so users can paste paths (including 8.3 short names)

Error Messages/Logs

Steps to Reproduce

1. Have a Windows user profile with spaces or hyphens in the path (e.g., C:\Users\Chris Duncanson-Hale)
2. Install Claude Desktop, subscribe to Max plan
3. Enable Hyper-V, HypervisorPlatform, VirtualMachinePlatform
4. Manually create NAT rule (since it is not auto-created): New-NetNat -Name "cowork-vm-nat" -InternalIPInterfaceAddressPrefix "172.16.0.0/24"
5. Start CoworkVMService: net start CoworkVMService
6. Open Claude Desktop → Cowork tab
7. Select any folder under the user profile
8. Observe: RPC error -1: failed to ensure virtiofs mount: Plan9 mount failed: bad address

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

Version 1.1.5368 (d12d02)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_