Summary

ChatGPT 5.1 introduces dual "brains" for instantaneous and advanced reasoning, offering more refined control over response generation. This distinction allows users to choose between a fast, default "Instant" mode for simple tasks like emails and summaries, or a more deliberate "Thinking" mode for complex problem-solving. The practical takeaway is greater flexibility and transparency, enabling users to optimize speed versus depth for a more efficient and intuitive AI experience.