OpenAI's o1 is a generative pre-trained transformer (GPT) model, designed for enhanced reasoning, especially in science and math. It uses a 'chain of thought' approach, spending more time "thinking" before answering, making it better at complex tasks. While not a successor to GPT-4o, o1 excels in scientific and mathematical benchmarks, and is trained with a new optimization algorithm. Different versions like o1-preview and o1-mini are available. Limitations include high computational cost, occasional "fake alignment," and a hidden reasoning process, and potential replication of training data.