their preferences， which can automatically decide whether to use its Chat or Thinking mode for your request. For complex tasks， as well as learned patterns from how people manually choose models， applying deeper reasoning before answering. The decision to “think longer” uses signals from your prompt and conversation， GPT-5 switches to GPT-5 Thinking，。

and how often the model’s answers are correct. ， ChatGPTs default model is GPT-5。