Milestones
- gpt-oss-120b and gpt-oss-20b released5 Aug 2025Complete.
- gpt-oss-safeguard safety classifiers released29 Oct 2025Complete.
Most important updates
- 29 Oct 2025
- 5 Aug 2025
Physics limits
- Shrinking numbers loses informationRunning on smaller hardware means storing weights in 4 to 8 bits instead of 16. Below about 4 bits accuracy drops quickly, so model size sets a floor on memory needed.
- Small models hold fewer factsMeasured knowledge capacity is about 2 bits of facts per parameter, so a 20B-parameter model simply cannot store what a trillion-parameter model can.
- Trained for likely text, not true textThe model learns to produce plausible words. Facts seen only once or twice in training can't be recalled reliably, so some rate of confident errors is built into the method.
How it works

Only a slice runs per word
gpt-oss-120b has 117B parameters but routes each token through experts totalling about 5.1B, so it is cheap to run for its size.
4-bit weights
Expert weights are stored in a 4-bit format (MXFP4), so the 120B model fits on one 80 GB GPU and the 20B model on a 16 GB machine.
Adjustable thinking
Like OpenAI's o-series it writes out reasoning first; users choose low, medium or high effort to trade speed for accuracy.
Weights you can keep
Released under Apache 2.0: anyone can download, modify and run the models privately, offline and on their own hardware.
Update log
Wed 29 Oct 2025
- Minor: BlogSoftware
Tue 5 Aug 2025
- Major: BlogSoftware
About OpenAI
OpenAI
ChatGPT, GPT models, Codex, Stargate
OpenAI makes ChatGPT and the GPT models behind it. ChatGPT's launch in November 2022 made AI chatbots mainstream. It also builds huge data centers through the Stargate project.
- Makes ChatGPT and the GPT-5.x models. GPT-5.6 came out in July 2026.
- Raised $122B at an $852B valuation in March 2026. Amazon, NVIDIA and SoftBank were the biggest investors.
- Lining up tens of gigawatts of computing power through Stargate and chip deals with NVIDIA, AMD and others.
- Founded
- 201511 yrs
- Headquarters
- United States
- Status
- Private
- Valuation
- $852BprivateMar 2026
- Raised
- $179B4 rounds
- Last round
- Venture round · $122BMar 2026$852B post
- Coverage
- 4 programs · 24 updateslatest 9 Jul 2026checked 25 Sep
- Lead investors
- AmazonNVIDIASoftBankThrive CapitalMicrosoft
- Partners
- Broadcom
- Investors
- MicrosoftSoftBankAmazon
- People
- Sam AltmanCEO and co-founderGreg BrockmanPresident and co-founderJakub PachockiChief Scientist

