GPT-OSS-20B

About

gpt-oss-20b (openai/gpt-oss-20b) is OpenAI's smaller open-weight model, released August 4, 2025 under Apache 2.0 alongside gpt-oss-120b - a 20.91B-parameter Mixture-of-Experts transformer with 3.61B activated parameters per token, a 131,072-token context, and text-only input/output. Its MoE weights are post-trained with MXFP4 quantization, letting the model run within 16GB of memory; all reported evals use that same quantization.

It shares the 120b feature set: configurable reasoning effort (low, medium, high) tuned to latency needs, fully exposed chain-of-thought (for debugging and trust, not for end users), native agentic capabilities (function calling, web browsing, Python code execution, Structured Outputs), and full fine-tunability. It was trained on a text-only dataset of trillions of tokens focused on STEM, coding and general knowledge (knowledge cutoff June 2024), with harmful content filtered via CBRN pre-training filters from GPT-4o; training required ~10x fewer H100-hours than gpt-oss-120b. Model card paper: arXiv 2508.10925.

Training Data Trained on a text-only dataset with trillions of tokens, with a focus on STEM, coding, and general knowledge. Knowledge cutoff: June 2024. Pre-training data filtered for harmful content using CBRN pre-training filters from GPT-4o. Training required ~10x fewer H100-hours than gpt-oss-120b.