[BUG] Code tab fails with "Host denied (verification failed)" on Windows 11 Insider Preview 26220 — VM never created, HCS error 0xC0370103

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 for this specific build
• [x] I am using the latest version of Claude Desktop (1.9659.4.0)

Environment

| Field | Value |
|---|---|
| Claude Desktop version | 1.9659.4.0 (MSIX) |
| Windows edition | Windows 11 Pro Insider Preview |
| Windows version | 25H2, Build 26220.8544 |
| CPU | Intel Core i7-11370H |
| Hyper-V | Enabled (Microsoft-Hyper-V-All) |
| Memory Integrity | Disabled (tested both on and off) |
| CoworkVMService | Running |
| vmms service | Running |
| hns service | Running |

What's wrong

The Code tab in Claude Desktop consistently fails with:

Connection failed: Host denied (verification failed)

Claude Desktop never creates the Cowork VM. The LocalState package folder is empty — no .vhdx disk image, no vm-info.json. Reinstalling from scratch does not resolve the issue.

Hyper-V Compute event log

The Host Compute Service starts successfully, but VM creation immediately fails with result 0xC0370103:

[cowork-vm-f47a0e65] Create compute system, result 0xC0370103
[cowork-vm-f47a0e65] Start compute system, result 0xC0370103

Error 0xC0370103 = ERROR_HV_CPUID_FEATURE_VALIDATION_ERROR

After disabling Memory Integrity and rebooting, the HCS log shows only:

The Host Compute Service is starting.

No VM creation is attempted at all — Claude Desktop appears to fail before even reaching the HCS layer.

Diagnostics

Get-HnsNetwork | Select-Object Name, Type
# Result: only "Default Switch" — cowork-vm-nat never created

Get-NetNat
# Result: no output (no NAT rules exist)

systeminfo | findstr /i "hyper-v"
# Result: A hypervisor has been detected. Features required for Hyper-V will not be displayed.

Get-WmiObject -Class Win32_Processor | Select-Object VirtualizationFirmwareEnabled
# Result: False (unreliable on this build — hypervisor IS present per systeminfo)

Steps to reproduce

1. Install Claude Desktop (MSIX) on Windows 11 Pro Insider Preview Build 26220
2. Sign in with a Pro account
3. Click the Code tab
4. Observe: "Connection failed: Host denied (verification failed)" immediately

Expected behavior

The Cowork VM should be created and the Code tab should connect successfully.

Additional notes

• Chat tab works normally
• Claude Code via WSL/terminal works normally
• Hyper-V was initially disabled; enabling it did not resolve the issue
• Disabling Memory Integrity (Core Isolation) did not resolve the issue
• Clean uninstall + reinstall did not resolve the issue
• This appears specific to Insider Preview Build 26220 — the VM provisioning step never executes

<img width="1446" height="967" alt="Image" src="https://github.com/user-attachments/assets/e369c1ad-ea15-4291-a55a-272bb740650c" />

What Should Happen?

Claude Code tab should be enabled

Error Messages/Logs

Here's the expanded logs section to add to the report:
## Error messages and logs

### Claude Desktop UI
Connection failed: Host denied (verification failed)

### Hyper-V Compute Operational log
### (Event Viewer > Applications and Services Logs >
###  Microsoft > Windows > Hyper-V-Compute > Operational)

First attempt (Memory Integrity on):
[cowork-vm-f47a0e65] Create compute system, result 0xC0370103
[cowork-vm-f47a0e65] Start compute system, result 0xC0370103
[cowork-vm-f47a0e65] Queue system notification: 5 / 0x00000000
[cowork-vm-f47a0e65] Queue system notification: 14 / 0x00000000
[cowork-vm-f47a0e65] Modify compute system (Plan9 shares for C:, D:, G:), result 0x00000000
[cowork-vm-f47a0e65] Queue system notification: 15 / 0x00000000
[cowork-vm-f47a0e65] Queue system notification: 2 / 0x00000000

After disabling Memory Integrity + reboot + clean reinstall:
The Host Compute Service is starting.
(No VM creation attempted at all — Claude Desktop fails before reaching HCS)

### PowerShell diagnostics

# No NAT rules exist
Get-NetNat
# (no output)

# cowork-vm-nat network never created
Get-HnsNetwork | Select-Object Name, Type
Name             Type
----             ----
Default Switch   ICS

# LocalState folder empty — no VM disk image created
Get-ChildItem "$env:LOCALAPPDATA\Packages\Claude_pzs8sxrjxfjjc\LocalState"
# (no output)

# Hypervisor is present but VM creation still fails
systeminfo | findstr /i "hyper-v"
Hyper-V Requirements: A hypervisor has been detected.
                      Features required for Hyper-V will not be displayed.


### Error code reference
0xC0370103 = ERROR_HV_CPUID_FEATURE_VALIDATION_ERROR
Hypervisor CPU feature validation failed during VM creation attempt.

Steps to Reproduce

Steps to reproduce

1. Have Windows 11 Pro Insider Preview Build 26220.8544 installed
2. Ensure Hyper-V is enabled (Microsoft-Hyper-V-All state: Enabled)
3. Ensure CoworkVMService, vmms, and hns are all running
4. Install Claude Desktop 1.9659.4.0 (MSIX) fresh — package family Claude_pzs8sxrjxfjjc
5. Sign in with a Pro account
6. Click the Code tab
7. Observe: "Connection failed: Host denied (verification failed)" immediately
8. Check %LOCALAPPDATA%\Packages\Claude_pzs8sxrjxfjjc\LocalState — folder is empty, no .vhdx or vm-info.json created
9. Check Hyper-V Compute event log — only "Host Compute Service is starting" entries, no VM creation attempted
10. Repeat with Memory Integrity (Core Isolation) disabled and rebooted — same result
11. Repeat with full uninstall (Remove-AppxPackage + delete Packages folder) and clean reinstall — same result

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.160 (Claude Code)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

Additional information

What DOES work on this machine

• Claude Desktop Chat tab — fully functional
• Claude Code via WSL2/Ubuntu terminal — fully functional
• WSL2 itself — running normally alongside Hyper-V

Hardware

• Device: Dell Inspiron 5482
• CPU: Intel Core i7-11370H (11th gen, supports VT-x and VT-d)
• VT-x enabled in BIOS firmware
• VT for Direct I/O enabled in BIOS firmware

Things tried that did not resolve the issue

• Multiple "Try again" clicks in the Code tab UI
• Signing out and back in to Claude Desktop
• Uninstall and reinstall (multiple times, including before Hyper-V was enabled)
• Enabling Hyper-V (was previously disabled — enabling it allowed first VM creation

attempt but still failed with 0xC0370103)

• Disabling Memory Integrity (Core Isolation) and rebooting
• Clean uninstall via Remove-AppxPackage + manual deletion of Packages folder,

followed by fresh install from claude.ai/download

Timeline

• June 1, 2026: First VM creation attempt logged (0xC0370103, Memory Integrity on)
• June 2, 2026: Hyper-V confirmed enabled, Memory Integrity disabled, clean reinstall

performed — VM creation no longer attempted at all after these changes