Introducing OpenAI’s gpt-oss: 20B & 120B Open-Weight Models for the Next Era of Local AI

OpenAI has taken a major step forward in democratizing advanced AI capabilities with the release of gpt-oss — a new family of open-weight models developed in partnership with Ollama.

These models, available in 20B and 120B parameter versions, are designed for powerful reasoning, agentic behaviors, and flexible integration into developer workflows. Most importantly, they can run locally and are licensed for commercial use under the permissive Apache 2.0 license.

In this post, we’ll break down what makes these models so special, how to get started, and why they mark a turning point for open AI development.

What Is gpt-oss?

gpt-oss stands for Open Source Series and includes two powerful large language models:

• gpt-oss:20b — 20 billion parameters, optimized for local, low-latency use.

• gpt-oss:120b — 120 billion parameters, designed for advanced agentic tasks and high-capacity reasoning.

They are released with open weights, meaning developers can download, run, and even fine-tune them for their specific needs.

Key Features at a Glance

• 128K Token Context Window

Work with extremely long inputs — such as full documents, codebases, or multi-step workflows — thanks to the extended 128,000-token context window.

• Agentic Capabilities

The models are built with agent-like behavior in mind, supporting function calling, tool use, web browsing, and structured outputs. With Ollama’s integration, they can behave like true autonomous assistants.

• Full Chain-of-Thought Reasoning

gpt-oss provides visibility into its reasoning process, which not only helps improve transparency but also simplifies debugging and tuning.

• Adjustable Reasoning Effort

You can control the “reasoning effort” level (low, medium, high), balancing response latency with depth of reasoning — ideal for performance-sensitive applications.

• Fine-Tuning Support

Both models are fully fine-tunable, enabling tailored behavior on domain-specific datasets, use cases, or tone of voice.

• Apache 2.0 License

No copyleft restrictions. Use it freely for commercial applications, modify it, build on top, and deploy as you wish — without worrying about patents or redistribution limitations.

Smarter Compression with MXFP4

To make these massive models easier to run locally, OpenAI introduced a new quantization format: MXFP4.

Thanks to this:

• gpt-oss:20b can run on systems with just 16GB of memory.

• gpt-oss:120b can fit entirely on a single 80GB GPU.

This is made possible with Ollama’s new engine, which natively supports MXFP4 without any conversions.

Getting Started with Ollama

Ollama offers the easiest way to run these models locally. After installing Ollama, simply launch the model via terminal:

ollama run gpt-oss:20b

or

ollama run gpt-oss:120b

This spins up the model on your machine — no cloud dependencies, no latency issues, and full control over your data and compute.

Which Model Should You Use?

Model	Parameters	Ideal For	Requirements
gpt-oss:20b	20B	Local chatbots, productivity tools, coding assistants	16GB RAM+
gpt-oss:120b	120B	Agent systems, deep reasoning, long-context apps	80GB GPU

Useful Links & References

• Ollama Website

• OpenAI Launch Blog

• MXFP4 Quantization Primer (NVIDIA)

Why This Matters

The release of gpt-oss represents a paradigm shift in how we build with AI:

• Researchers get full transparency and access.

• Developers can run powerful LLMs offline or on the edge.

• Enterprises gain fine-tuned control and data privacy.

• The open-source community gets a model that's actually usable.

In an era where foundation models are becoming central to apps, assistants, and tools — the ability to run open, local, powerful models is game-changing.

Whether you're building a coding assistant, integrating an LLM into your product, or experimenting with AI agents, gpt-oss offers a production-ready foundation with complete freedom.

It’s never been easier to run and customize a state-of-the-art model on your own hardware.

ollama run gpt-oss:20b

The future of AI isn't just in the cloud — it's in your hands.

Let me know if you need further clarification or additional steps!