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On our own GPUs

gpt-oss-120b API

OpenAI’s own open-weight reasoning model, under Apache 2.0.

  • Context

    128K

  • Max output

    32K

  • Serving precision

    BF16 / MXFP4

  • Licence

    Apache-2.0

gpt-oss-120b is OpenAI’s open-weight reasoning model, released under Apache 2.0 with a 128K context window. It uses a mixture-of-experts architecture with a small active parameter count, which is why it fits on a single high-end accelerator and why its unit cost lands so low. For bulk, stable, inexpensive inference it remains one of the most pragmatic choices in the open-weight camp.

Open weights, deployed in facilities we build out and lease directly, operated by us. We resell nobody else’s account quota.

Specifications

Model ID
gpt-oss-120b
Published by
OpenAI
How it is served
On our own GPUs
Licence
Apache-2.0
Total parameters
120B MoE
Active parameters
5.1B
Context
128K
Max output
32K
Serving precision
BF16 / MXFP4
Input modalities
Text
Released
2025-08-05

What it is good at

A reasoning model that stays cheap
It emits chain-of-thought yet keeps unit cost low thanks to a small active parameter count. For work that needs some reasoning depth at high throughput, the economics are hard to beat.
Apache 2.0, no strings
No restrictions on commercial use, modification or redistribution, and no user-count clause. We can run it legally in our own facilities, and you can stand up the same weights yourself as a control.
A mature ecosystem
Released early and widely adopted, so quantisation recipes, serving frameworks and fine-tuning toolchains are all well trodden. Fewest surprises if you want a private deployment or a side-by-side comparison.

Where it fits

  • High-volume classification, extraction and rewriting
  • Pipelines that need some reasoning depth on a tight budget
  • Local or edge deployments as a control or fallback
  • A baseline for evaluating open-model capability

Three steps

Change one line of base_url, put the model ID below in the `model` field, and leave the rest of your code alone.

model: "gpt-oss-120b"

curl https://api.nexaix.net/v1/chat/completions \
  -H "Authorization: Bearer $NEXAIX_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "gpt-oss-120b",
    "stream": true,
    "messages": [
      { "role": "user", "content": "Summarise this contract." }
    ]
  }'

About this model

Is gpt-oss the same thing as GPT-5?

No. gpt-oss is a separate open-weight series whose weights can be downloaded and deployed freely; the GPT-5 family is proprietary and reachable only through an official commercial channel. Different capability tiers and different purposes.

Is a 128K window enough?

For the vast majority of production work, yes. When you need more, GLM-5.2, DeepSeek V4 and Kimi K3 are all on the fleet with 1M-token windows.

What precision do you serve?

The precision we currently serve is published on this page. gpt-oss also ships an MXFP4 quantised build; we will not silently swap to a lower-precision variant — that is exactly the "silent downgrade" we refuse to do.

Also worth a look

Run your own eval on it

Take the trial credit, run the evals you already have against this model, and then decide whether it gets your production traffic.