Responses API fails with `background:true` when an MCP tool is used ― works fine synchronously

API
1

Hi everyone,

I’m seeing consistent failures when I set "background": true on the /v1/responses endpoint and include an external MCP tool.
Without background mode the same request succeeds every time.

What I’m doing

// Supabase Edge Function (simplified)
const payload = {
  prompt: { id: PROMPT_ID },
  tools: [
    {
      type: "mcp",
      server_label: "Zapier",
      server_url: `https://mcp.zapier.com/api/mcp/mcp`,
      headers: { Authorization: `Bearer ${ZAPIER_API_KEY}` },
      allowed_tools: ["gmail_find_email", "gmail_reply_to_email"],
      require_approval: "never"
    }
  ],
  input: [{ role: "user", content: [{ type: "input_text", text: query }] }],
  background: true            // ← removing this makes everything work
};

await fetch("https://api.openai.com/v1/responses", {
  method: "POST",
  headers: {
    "Content-Type": "application/json",
    Authorization: `Bearer ${OPENAI_API_KEY}`
  },
  body: JSON.stringify(payload)
});

Symptoms

  • API returns generic error:
    An error occurred while processing your request. You can retry your request, or contact us…
    Example request-id: wfr_0197bad74a6f79f29585a003c7f306dd

  • My webhook receives:
    response.failed with no additional details.

  • In the dashboard the run never leaves queued / in_progress before it flips to failed.

  • Removing only "background": true (keeping everything else, same prompt, same MCP tool) returns a perfect response.

Repro in cURL (minimal)

curl https://api.openai.com/v1/responses \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer $OPENAI_API_KEY" \
  -d '{
        "tools": [{
          "type": "mcp",
          "server_label": "Zapier",
          "server_url": "https://mcp.zapier.com/api/mcp/mcp",
          "headers": {"Authorization": "Bearer REDACTED"},
          "require_approval": "never"
        }],
        "input": "test",
        "background": true
      }'

→ Always fails.
Delete the background line → returns normally.

Things I’ve already checked

  • store:true is implicit for background runs, so not the issue.
  • Same behaviour with stream:true both on and off.
  • Works if I swap the tool for an OpenAI-native tool (Web Search, for example).
  • Tried different MCP servers – same result.
  • Tried different models (o3, gpt-4.1, gpt-4o) – same result.

Hypothesis

Looks like the background runner can’t open the remote transport for MCP tools.

Would love confirmation that this is a known bug and — if possible — an ETA or suggested workaround.

Thanks!

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