Structured Output problem

[NovaH00]

When I use the OpenAI Python SDK with the llama-server endpoint, I couldn't get the response_format to work!

# llm.py
from openai import OpenAI
from pydantic import BaseModel

client = OpenAI(base_url="http://localhost:8080", api_key="unused")

class CalendarEvent(BaseModel):
    name: str
    date: str
    participants: list[str]

response = client.chat.completions.parse(
    model="gpt-oss-20b",
    messages=[
        {
            "role": "system", 
            "content": "Extract the event information."
        },
        {
            "role": "user",
            "content": "Alice and Bob are going to a science fair on Friday.",
        },
    ],
    response_format=CalendarEvent,
)

print(response)

$ uv run llm.py
...
openai.InternalServerError: Error code: 500 - {'error': {'code': 500, 'message': 'Failed to parse input at pos 610: <|start|>assistant<|channel|>final<|message|>**Event Information**\n\n- **Event**: Science Fair  \n- **Date**: Friday  \n- **Participants**: Alice, Bob', 'type': 'server_error'}}

I found some issues related to this problem and it seem like they all fixed but I don't really know why it's not working

Also I intercepted the payload send by the SDK

{
  "messages": [
    {
      "role": "system",
      "content": "Extract the event information."
    },
    {
      "role": "user",
      "content": "Alice and Bob are going to a science fair on Friday."
    }
  ],
  "model": "gpt-oss-20b",
  "response_format": {
    "type": "json_schema",
    "json_schema": {
      "schema": {
        "properties": {
          "name": {
            "title": "Name",
            "type": "string"
          },
          "date": {
            "title": "Date",
            "type": "string"
          },
          "participants": {
            "items": {
              "type": "string"
            },
            "title": "Participants",
            "type": "array"
          }
        },
        "required": [
          "name",
          "date",
          "participants"
        ],
        "title": "CalendarEvent",
        "type": "object",
        "additionalProperties": false
      },
      "name": "CalendarEvent",
      "strict": true
    }
  },
  "stream": false
}

Some issue mentioning the fix is to use json_object rather than json_schema but I tried using curl with that and got no luck.