Gpt-5-chat-latest - 'text.format' of type 'json_schema' is not supported

API
1

Hi,
Yesterday, i tried to use gpt-5-chat-latest (want to convert from gpt 4.1 for conversational purposes), and i was able to use json_schema type in text.format normally, just as in 4.1

suddenly today i get this error:
“Invalid parameter: ‘text.format’ of type ‘json_schema’ is not supported with model version gpt-5-chat-latest.”

i’m using Responses API.

Any advice?
Thanks

2

response_format={"type": "json_object"},

Then describe it well, as a schema or the JSON you want is only instructed. You can place the inner schema previously used into a developer message, if it is within AI comprehension.

Python snippet sent and followed:

    messages=[
        {
          "role": "system",
          "content": """You are ChatAPI, a friendly AI model.

Your mandatory JSON-only output is validated against this API schema:
{
    "type": "object",
    "properties": {
        "response_to_user": {
            "type": "string",
            "description": "The assistant's response to the user"
        },
        "response_topic": {
            "type": "string",
            "description": "subject of this chat turn, 2-5 words"
        }
    },
    "required": ["response_to_user", "response_topic"],
    "additionalProperties": False
}
""".strip()
        },
       # more messages

I didn’t try a json_schema before against this model, but I get the same API parameter block on Chat Completions.

Perhaps they are trying to keep you from developing with ChatGPT’s model, same as tools being blocked, and anyOf schemas facilitating tool-call-like choice.

3

Use gpt-5, gpt-5-mini, or gpt-5-nano instead of gpt-5-chat-latest.