What is the difference between chain-of-thought and reasoning models?

Chain-of-thought is a prompting technique that any general-purpose LLM can use. Reasoning models like OpenAI o1, o3, and Claude with extended thinking are trained specifically to perform internal reasoning before responding, often using reinforcement learning on math and code. Reasoning models produce far better results on hard problems but cost more, respond more slowly, and do not need explicit CoT prompting.