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gpt-oss

by OpenAIUS

DeployStage 4 of 5

Two open-weight reasoning models released in August 2025 under a permissive licence.

Updated 29 Oct 2025Checked 25 Sep0 updates this week

Milestones

No announced next step
  1. gpt-oss-120b and gpt-oss-20b released5 Aug 2025Complete.
  2. 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

4 parts
A GeForce RTX graphics card inside a desktop PC: the smaller gpt-oss model runs on a single consumer GPU like this
A GeForce RTX graphics card inside a desktop PC: the smaller gpt-oss model runs on a single consumer GPU like thisPhoto: Christian Wiediger · Unsplash License (opens unsplash.com)
Experts

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.

Compression

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.

Reasoning

Adjustable thinking

Like OpenAI's o-series it writes out reasoning first; users choose low, medium or high effort to trade speed for accuracy.

Licence

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

2 updates

Wed 29 Oct 2025

  • Minor: BlogSoftware

Tue 5 Aug 2025

  • Major: BlogSoftware

About OpenAI

The team behind gpt-oss

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
Works in
AIFrontier modelsComputing
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
Primer