[Bug]: Anthropic structured output (response_format.json_schema) fails with "output_config.format.name: Extra inputs are not permitted"

[adilson0888]

What happened?

Any request to the anthropic provider using structured JSON output — response_format.json_schema on /v1/chat/completions, or text.format on /v1/responses — fails with a 400 from the real upstream Anthropic API:

{"type":"error","error":{"type":"invalid_request_error","message":"output_config.format.name: Extra inputs are not permitted"},"request_id":"req_011Ce2pcdhDimKeeDjRZViSw"}

Root cause

src/upstream/translator.ts builds the outbound Anthropic request as:

anthropicBody.output_config = {
  format: {
    type: "json_schema",
    schema: fmt.json_schema.schema,
    name: fmt.json_schema.name,   // <-- rejected by Anthropic
  },
};

Anthropic's Messages API output_config.format only accepts { type, schema } — it has no name field (unlike OpenAI's json_schema.name / text.format.name, which this code is clearly translating from). Sending the extra field trips Anthropic's strict schema validation and every structured-output request to the anthropic provider fails outright.

This hits both translator paths that build Anthropic requests:

• openaiToAnthropic (Chat Completions → Anthropic) — line ~200
• responsesToAnthropic (Responses API → Anthropic) — line ~579

(The equivalent OpenAI-Responses-shaped output in chatToResponsesRequest / text.format.name is unaffected — that field is valid for OpenAI's own Responses API and is a separate code path.)

Steps to reproduce

1. Log in with --provider=anthropic.
2. Send a chat completion with a JSON-schema response format, e.g. (this is the exact request that reproduced it, via Karakeep's auto-tagging feature):

curl -s http://127.0.0.1:8317/v1/chat/completions \
  -H "Authorization: Bearer $KEY" -H "Content-Type: application/json" \
  -d '{
    "model": "claude-haiku-4-5",
    "messages": [{"role":"user","content":"Extract tags for: a tutorial about docker compose networking"}],
    "response_format": {
      "type": "json_schema",
      "json_schema": {
        "name": "tags",
        "schema": {"type":"object","additionalProperties":false,"properties":{"tags":{"type":"array","items":{"type":"string"}}},"required":["tags"]}
      }
    }
  }'

3. Observe the 400 above instead of a completion.

Fix

PR incoming: drops the name field from both output_config.format construction sites. Verified against the live Anthropic API — same request as above now returns a real completion instead of a 400. Also updated tests/unit.test.ts, which had a stale assertion (`result.output_config.format.name === "test"") enshrining the buggy shape.

What LiteLLM/auth2api version are you on?

Reproduced against main as of 2026-08-14.

Twitter / LinkedIn details

No response