responseFormat

An object specifying the format that the model must output.

Setting to ChatResponseFormat.JsonObject enables JSON mode, which guarantees the message the model generates is valid JSON.

Important: when using JSON mode, you must still instruct the model to produce JSON yourself via some conversation message, for example, via your system message. If you don't do this, the model may generate an unending stream of whitespace until the generation reaches the token limit, which may take a lot of time and give the appearance of a "stuck" request. Also note that the message content may be partial (i.e., cut off) if finish_reason="length", which indicates the generation exceeded max_tokens or the conversation exceeded the max context length.