responseFormat

Specifies the format that the model must output. Compatible with GPT-4o, GPT-4 Turbo, and all GPT-3.5 Turbo models since gpt-3.5-turbo-1106.

Setting to AssistantResponseFormat.JSON_SCHEMA enables Structured Outputs which ensures the model will match your supplied JSON schema.

Structured Outputs (AssistantResponseFormat.JSON_SCHEMA) are available in our latest large language models, starting with GPT-4o:

1. gpt-4o-mini-2024-07-18 and later

2. gpt-4o-2024-08-06 and later

Older models like gpt-4-turbo and earlier may use JSON mode (AssistantResponseFormat.JSON_OBJECT) instead.

Setting to AssistantResponseFormat.JSON_OBJECT enables 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.