OpenAI on Tuesday released two open-weight language models for the first time since it rolled out GPT-2 in 2019.

The text-only models are called gpt-oss-120b and gpt-oss-20b, and are designed to serve as lower-cost options that developers, researchers and companies can easily run and customize, OpenAI said.

An artificial intelligence model is considered open weight if its parameters, or the elements that improve its outputs and predictions during training, are publicly available. Open-weight models can offer transparency and control, but they are different from open-source models, whose full source code becomes available for people to use and modify.

Several other tech companies, including Meta, Microsoft-backed Mistral AI and the Chinese startup DeepSeek, have also released open-weight models in recent years.

“It’s been exciting to see an ecosystem develop, and we are excited to contribute to that and really push the frontier and then see what happens from there,” OpenAI President Greg Brockman told reporters during a briefing.

The company collaborated with Nvidia, Advanced Micro Devices, Cerebras, and Groq to ensure the models will work well on a variety of chips.

“OpenAI showed the world what could be built on Nvidia AI — and now they’re advancing innovation in open-source software,” Nvidia CEO Jensen Huang said in a statement.

The release of OpenAI’s open weight models has been highly anticipated, in part because the company repeatedly delayed the launch.

In a post on X in July, OpenAI CEO Sam Altman said the company needed more time to “run additional safety tests and review high-risk areas.” That came after a separate post weeks earlier, where Altman said the models would not be released in June.

OpenAI said Tuesday that it carried out extensive safety training and testing on its open-weight models.

It filtered out harmful chemical, biological, radiological and nuclear data during pre-training, and it mimicked how bad actors could try to fine-tune the models for malicious purposes. Through this testing, OpenAI said it determined that maliciously fine-tuned models were not able to reach the “high capability” threshold in its Preparedness Framework, which is its method for measuring and protecting against harm.

The company also worked with three independent expert groups who provided feedback on its malicious fine-tuning evaluation, OpenAI said.

OpenAI said people can download the weights for gpt-oss-120b and gpt-oss-20b on platforms like Hugging Face and GitHub under an Apache 2.0 license. The models will be available to run on PCs through programs such as LM Studio and Ollama. Cloud providers Amazon, Baseten and Microsoft are also making the models available.

Both models can handle advanced reasoning, tool use and chain‑of‑thought processing, and are designed to run anywhere — from consumer hardware to the cloud to on-device applications.

Users can run gpt-oss-20b on a laptop, for instance, and use it as a personal assistant that can search through files and write, OpenAI said.

“We’re excited to make this model, the result of billions of dollars of research, available to the world to get AI into the hands of the most people possible,” Altman said in a statement Tuesday.

–CNBC’s Jordan Novet contributed to this report

The U.S. should deploy a small nuclear power plant to the surface of the moon before China and Russia are able to do so, the interim head of NASA has told the space agency’s staff.

NASA should be ready to launch a reactor to the lunar surface by the first quarter of fiscal year 2030, Transportation Secretary Sean Duffy, who is serving as the space agency’s acting administrator, said in a directive to NASA dated July 31. This would work out to late 2029.

China and Russia are aiming to deploy a reactor to the moon by the mid-2030s to power a joint base, officials in Moscow and Beijing have said. The first country to deploy a reactor on the moon “could potentially declare a keep-out zone which would significantly inhibit the United States from establishing a planned Artemis presence if not there first,” Duffy warned NASA. The Artemis mission is NASA’s lunar exploration program, which was first announced in 2017.

NASA should issue a request for proposals to industry within 60 days, according to Duffy’s directive. The reactor should be able to generate 100 kilowatts of electricity at a minimum, according to the directive. It would be transported aboard a heavy class lander with a payload of 15 metric tons.

A reactor without a 100-kilowatt output could power about 80 U.S. homes. By contrast, the average nuclear reactor in the U.S. fleet can power more than 700,000 homes.

The NASA program, called Fission Surface Power, will rely on microreactor technology, according to Duffy’s directive. But no microreactor has been licensed by the Nuclear Regulatory Commission, let alone built in the U.S. President Donald Trump issued a series of executive orders in May that aim to expedite the commercialization of small nuclear reactors.

Duffy’s ambitious directive comes as the Trump administration has proposed steep cuts to NASA’s budget. The space agency also remains without a Senate-confirmed leader. Trump named Duffy as acting administrator after pulling his original nominee in May amid a feud with SpaceX CEO Elon Musk.

Politico first reported Duffy’s plans to launch a nuclear reactor to the moon.