OpenAI's first open-weight LLMs since GPT-2 (2019). Apache 2.0 license. Trained with RL and distillation from o3 and frontier internal models. GPT-oss-120B runs on single 80GB GPU; 20B runs on 16GB edge devices.

Flagship reasoning model with adaptive tool-use -- intelligently invokes retrieval and code interpreter on demand during inference. Advanced test-time scaling via RL.