Secure MCP Tunnel returns 424 in Responses API

API
,
1

Hi OpenAI Support,

I am testing Secure MCP Tunnel with the Responses API.

The tunnel-client is running and healthy/ready. tunnel-client doctor --explain passes, and the local MCP server starts successfully over stdio: Secure MCP Filesystem Server running on stdio

The tunnel-client debug logs show long polling is active, but no commands are received:

{
  "level": "DEBUG",
  "msg": "poll cycle complete",
  "tunnel_id": "tunnel_xxxx",
  "component": "controlplane",
  "commands_polled": 0,
  "commands_enqueued": 0
}

Responses API config:

{
  model: "gpt-5",
  tools: [
    {
      type: "mcp",
      server_label: "main",
      server_url: "https://api.openai.com/v1/mcp/tunnel_xxx",
      require_approval: "never"
    }
  ],
  input: "List all the MCP tools you have access to. Just list the tool names and a brief description"
}

Log:

[04:18:38.989] Chunk #1: response.created
� Response created: resp_0ce7b708ed2c268e006a33719eb0908198ae55580b081afe60
[04:18:38.990] Chunk #2: response.in_progress
[04:18:38.990] Chunk #3: response.output_item.added
:plus: Output item added: mcp_list_tools
[04:18:38.991] Chunk #4: response.mcp_list_tools.in_progress
[04:18:38.991] Chunk #5: response.mcp_list_tools.failed
Full error: {
“headers”: {},
“requestID”: “req_4b3609f752d647bdb5d023dc3f1e8bbf”,
“error”: {
“type”: “external_connector_error”,
“code”: “http_error”,
“message”: “Error retrieving tool list from MCP server: ‘main’. Http status code: 424 (Failed Dependency)”,
“param”: “tools”
},
“code”: “http_error”,
“param”: “tools”,
“type”: “external_connector_error”
}
:cross_mark: TEST FAILED: Error retrieving tool list from MCP server: ‘main’. Http status code: 424 (Failed Dependency)

I have already verified that the API keys and tunnel are in the same organization, and the runtime key has Tunnels:Read and Tunnels:Use. I also tried a caller API key with tunnel permissions, but the issue remains.

Could you please check whether this tunnel is correctly associated/enabled for Responses API MCP usage, and whether /v1/mcp/{tunnel_id} is being routed to the tunnel control-plane queue correctly?

Thanks.