[BUG] Cowork VM boots but API is UNREACHABLE - Windows 11 Pro 24H2

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 VM boots but API is UNREACHABLE - Windows 11 Pro 24H2

Preflight Checklist

• [x] I have searched existing issues and this hasn't been fully resolved
• [x] This is a single bug report
• [x] I am using the latest version of Claude Desktop
• Version 1.1.3363 (ee4247)

Related Issues

• #24945 - Cowork VM boots but API unreachable on Windows 11
• #25155 - Cowork Windows VM boots but cannot reach Claude API (Windows 10 Pro, Hyper-V)
• #25205 - Cowork API connection issue + Cowork Tab disappears on restart
• #25308 - Cowork VM starts but API is UNREACHABLE on Windows 11

Environment

• OS: Windows 11 Pro, Version 24H2, OS Build 26100.7623
• Claude Desktop Version: Latest (as of Feb 2026)
• Hyper-V: Enabled
• Antivirus/EDR: Windows Defender only

What's Wrong?

Cowork tab consistently fails with "Failed to start Claude's workspace - Can't reach the Claude API from Claude's workspace." Regular Chat mode works perfectly. The Hyper-V VM boots and gets CONNECTED network status, but API reachability always goes PROBABLY_UNREACHABLE then UNREACHABLE.

Actual Behavior

Error sequence:

1. "Sorry, it's taking a while to connect to the Claude API... Taking longer than expected to reach the Claude API. Still trying."
2. "Failed to start Claude's workspace - Can't reach the Claude API from Claude's workspace. Restarting Claude or reconnecting to your network sometimes resolves this."

What Should Happen?

Expected Behavior

Cowork workspace should start successfully and connect to the Claude API, allowing task execution -- identical to how Chat mode works.

Error Messages/Logs

## Diagnostics

### Network Adapter

vEthernet (cowork-vm-nat) exists with IP 172.16.0.1/24
Forwarding: Enabled
Wi-Fi Forwarding: Enabled (manually set)


### NAT Rule

Get-NetNat
# Returns existing rule (duplicate error on manual New-NetNat confirms it exists)


### Routing Table (cowork adapter)

DestinationPrefix             NextHop   RouteMetric
172.16.0.0/24                 0.0.0.0         256
172.16.0.1/32                 0.0.0.0         256
172.16.0.255/32               0.0.0.0         256
0.0.0.0/0                     0.0.0.0          10   <-- NextHop is 0.0.0.0, not 172.16.0.1


### Firewall Rules
No cowork-specific rules exist by default. Manually added outbound allow rule for vEthernet (cowork-vm-nat) on TCP/443 -- did not resolve the issue.

### Adapter Statistics (VM is sending traffic)

Name                          ReceivedBytes  SentBytes
vEthernet (cowork-vm-nat)        835542       2625894


## Troubleshooting Already Attempted
- Exit/quit Claude from system tray and restarted
- Network reconnect
- Verified host can reach api.anthropic.com (confirmed working via Chat)
- Confirmed Hyper-V is enabled
- Verified WinNAT rule exists
- Manually enabled IP forwarding on cowork adapter
- Manually enabled IP forwarding on Wi-Fi adapter
- Added explicit outbound firewall allow rule for cowork adapter on TCP/443
- Attempted to add default route with NextHop 172.16.0.1 (fails with "already exists" -- app creates it with NextHop 0.0.0.0 which is a null route)

## Root Cause Hypothesis
The app creates the default route `0.0.0.0/0` on the cowork adapter but sets NextHop to `0.0.0.0` instead of the gateway `172.16.0.1`. This makes it a null/black-hole route -- the VM has no valid path to the internet. Manual correction fails because the app-created route blocks re-creation. This matches the pattern described in #25155.

## Workaround
None found via manual network configuration. Currently using Claude Code CLI in WSL2 as a substitute.

Steps to Reproduce

Steps to Reproduce

1. Install latest Claude Desktop on Windows 11 Pro 24H2 with Hyper-V enabled
2. Sign in with a paid subscription
3. Click the Cowork tab
4. Observe: VM downloads, boots, connects to network, then fails API reachability check

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

Version 1.1.3363 (ee4247)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

_No response_