OpenAI has released two new open-source models, gpt-oss-20b and gpt-oss-120b, which mark the organization's return to open models after GPT-2. These models are designed for strong reasoning and problem-solving, with features that include long context windows, adjustable reasoning levels, and support for both built-in and user-provided tools. They are particularly suited for agentic use cases due to their ability to generate consistent multi-turn trajectories and their standard mixture-of-experts transformer architecture, enhanced through focused training data and reinforcement learning. The models are benchmarked against other OpenAI models and Chinese proprietary models, showing competitive performance even with smaller sizes. Additionally, OpenAI introduces the Harmony Chat Format, a new chat protocol that enhances the models' interactive capabilities, allowing for structured problem-solving and advanced agentic tasks. These models can be deployed on Fireworks AI and are part of a collaboration with AMD to make AI models more accessible and cost-efficient on AMD's latest GPUs.