Despite the company's name, OpenAI hasn't dropped an open version of its AI models since GPT-2 in 2019. That changed on Tuesday, as CEO Sam Altman shared two new open-weights, reasoning AI models, named gpt-oss-120b (120 billion parameters) and gpt-oss-20b (20 billion parameters).

To understand why this is such a big deal, it helps to understand the difference between closed models and open models. Closed models, such as OpenAI’s o models or Anthropic’s