Used to enable JSON mode, which guarantees the message the model generates is valid JSON.
Important: when using JSON mode, you must also instruct the model to produce JSON yourself
via a system or user message. Without this, the model may generate an unending stream of
whitespace until the generation reaches the token limit, resulting in a long-running and
seemingly "stuck" request. Also note that the message content may be partially cut off if
finish_reason="length", which indicates the generation exceeded max_tokens or the
conversation exceeded the max context length.
The chat response format parameters.