OpenAI rediscovers an open AI mission, with new reasoning models

It was a long wait since the GPT-2 in 2019, but OpenAI is now releasing its newest open-weight large language models (LLMs). They’ve been dubbed GPT-OSS, the current lot consisting of gpt-oss-120b and gpt-oss-20b, dubbed “reasoning models” with OpenAI claiming these models outperform similarly sized open models on reasoning tasks. The importance of this brings OpenAI back, in a way, to their original mission of building AI systems that benefit all of humanity. Over the years, the artificial intelligence (AI) company has faced criticism of distraction towards that stated mission, as competition escalated rapidly.

OpenAI has not released open source models. (Official Image)

“Releasing gpt-oss-120b and gpt-oss-20b marks a significant step forward for open-weight models. At their size, these models deliver meaningful advancements in both reasoning capabilities and safety. Open models complement our hosted models, giving developers a wider range of tools to accelerate leading edge research, foster innovation and enable safer, more transparent AI development across a wide range of use cases,” the company says, in a statement.

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Two questions that need to be answered before we get into the specifics of gpt-oss-120b and gpt-oss-20b models. First, what are open weight LLMs and are they different from LLMs you regularly use? And secondly, what are reasoning models? The former is best defined as a large language model that is released by a company publicly, in its entirety, which means all the actual model weights (read this as parameters, defined by billion or “b” in model names) and any user can download these models completely on their own hardware.

In comparison, the most popular LLMs that you may have used, including OpenAI’s own GPT models as well as the likes of Google Gemini 2.5 and Anthropic’s Claude Sonnet 4, are closed models — that means they are accessible through an application layer while the model weights are not in the public domain. At the same time, Meta’s Llama models, as well as certain models by Mistral, have followed the open weight methodology, in recent times.

Open weight AI models are not to be confused with open source models however, the fine difference being that the latter models such as the DeepSeek R1 also make training code, datasets, and linked documentation available publicly — open weight models don’t. Having the training code and data sets allows a user or developer to retrain an open-source model from scratch, often for customised usage scenarios. That flexibility isn’t there for open weight models, though accessible in their entirety. OpenAI has not released open source models.

To the second question, reasoning models slightly differ from a few other LLMs in the sense that they are specifically designed to spend more time “thinking through” complex problems before generating their final response. They are expected to use extended reasoning processes to work through multi-step problems.

Back to gpt-oss-120b and gpt-oss-20b, and the primary difference is in the number of parameters each has. Parameters are essentially like the strength of synapses in a human brain, which determines how strongly different “neurons” influence each other, before providing an answer for a query. In OpenAI’s naming scheme this time, there is a slight confusion — the gpt-oss-120b is a 117 billion parameter model, while the smaller gpt-oss-20b has 21 billion parameters.

OpenAI’s benchmark scores do peg the gpt-oss-120b and gpt-oss-20b close to the o3 and o4-mini models in most tests. Take for instance the MMLU benchmark, which consists of questions across academic disciplines — the gpt-oss-120b returned 90% accuracy while gpt-oss-20b clocked 85.3% accuracy; in comparison, the o3 (93.4%), o4-mini (93%) and o3-mini (87%) bookend the new open weight models.

Just in case you are wondering about the memory requirements for downloading and running these open weight models on your computing device, OpenAI confirms that the gpt-oss-120B model will need 80GB of memory on the system, while gpt-oss-20b requires at least 16GB. They say that Microsoft is also bringing GPU-optimised versions of the gpt-oss-20b model to Windows devices.