MiniMax M2.5 rejects Claude Code background structured-output requests (HTTP 400 invalid params)

[alex-feel]

Hi MiniMax team,

This issue has been affecting us for more than a month, and it still appears unresolved.

minimax-m2.5 returns HTTP 400 with:

{
  "type": "error",
  "error": {
    "type": "invalid_request_error",
    "message": "invalid params"
  }
}

for a valid Claude Code background request pattern.

Important context:

• This is not a user-typed prompt flow in the UI.
• This is a background/service request sent by Claude Code for internal tasks (for example, background title-generation / structured-output utility calls).
• Regular visible user chat requests can work, while these background requests fail.

This strongly suggests the API does not fully support recent Claude Code request formats.

Repro (sanitized)

1. Send a POST /v1/messages request with model: "minimax-m2.5".
2. Use normal messages + system.
3. Include structured output config in Anthropic-compatible form:

{
  "output_config": {
    "effort": "medium",
    "format": {
      "type": "json_schema",
      "schema": {
        "type": "object",
        "properties": {
          "title": { "type": "string" }
        },
        "required": ["title"],
        "additionalProperties": false
      }
    }
  },
  "stream": true
}

4. Observe HTTP 400 invalid_request_error / invalid params.

Expected behavior

minimax-m2.5 should accept this request shape and process it, since this background flow is part of current Claude Code behavior.

Actual behavior

The request is rejected with HTTP 400, which breaks background service calls even when user-visible requests appear fine.

Impact

• Breaks Claude Code background functionality (not visible directly in UI, but required for a complete integration).
• Appears account-independent in our testing and affects all environments we tried.
• Causes recurring operational errors with no actionable parameter-level diagnostics.

Request

1. Please add support for this structured-output/background request pattern for minimax-m2.5.
2. Please improve validation errors to identify the exact incompatible field(s), instead of generic invalid params.
3. Please verify API monitoring/alerting for this failure class (invalid_request_error on background structured-output calls), because this has persisted for over a month.

If needed, we can provide additional sanitized traces (request IDs, timestamps, and reduced payloads) to help your team reproduce quickly.