GPT-5.4 Thinking is OpenAI’s reasoning-focused model available on ChatGPT’s paid tiers (Plus, Pro, Business, Enterprise, Edu). It takes additional time to think through complex problems before responding, delivering deeper analysis on tasks like math, science, code, and multi-step reasoning.
Unlike the default Instant model, Thinking explicitly trades latency for better answers on harder problems — useful for technical questions, debugging, research, and tasks that benefit from a step-by-step approach.