Which ChatGPT version is best? A guide on the difference between all of OpenAI's models.

Former OpenAI employee, Suchir Balaji, died by suicide late last month. He was part of a key copyright lawsuit that could have far-reaching implications for AI models like ChatGPT.

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• OpenAI has released numerous models with a confusing pattern of names over the past few years.
• It has developed both large language models like GPT-5 and GPT-4.5 and reasoning models like o1.
• Here's a guide on what makes each one unique.

ChatGPT isn't a monolith.