Run gpt-oss-120b in the EU through an OpenAI-compatible API

gpt-oss-120b is one of two open-weight models OpenAI released in August 2025. It is a mixture-of-experts model with 117 billion parameters, of which 5.1 billion are active for each token, and a context window of 128K tokens. Its expert weights were post-trained in MXFP4 precision, which lets the full model run on a single 80 GB GPU.

It is a reasoning model: before answering it works through the problem in a chain of thought, and you choose the reasoning effort per request, from low for quick replies to high for careful analysis. It was trained on OpenAI's harmony response format and supports function calling and structured outputs. It handles text only.

gpt-oss-120b is strong at reasoning, maths, coding and tool use for its active size, and it is a natural first step for teams moving off OpenAI's hosted models: the behaviour and prompt style feel familiar, and structured outputs and function calling work the way OpenAI users expect. The low number of active parameters keeps it efficient.

It does not accept images or audio. Its knowledge is older than that of 2026 models such as Qwen3.8 or DeepSeek V4, which beat it on many agentic coding tasks. OpenAI does not publish a list of supported languages on the model card, so test European languages on your own content. High reasoning effort can produce many output tokens.

If you use the OpenAI SDK today, switching is two lines: set the base URL to the inference.eu API and use your inference.eu key. Then set the model to gpt-oss-120b. The harmony format is handled on our side, so you send ordinary chat messages and receive ordinary responses.

Set reasoning_effort to low, medium or high to trade speed against depth. Tool calls, JSON schema outputs and streaming work as usual. The model's chain of thought is meant for debugging rather than for end users, so show only the final answer in your product. The Anthropic Messages format is available as well.

Using gpt-oss-120b on inference.eu is not the same as using OpenAI's own API. The open weights run on infrastructure in the European Union, your prompts and the responses are processed in EU data centres, nothing is sent to OpenAI, and nothing is used to train any model.

Every customer receives a data processing agreement under Article 28 of the GDPR and our list of subprocessors, so there is no transfer of prompts to the United States to assess. Billing is in euros. The Apache 2.0 licence allows commercial use without user limits; OpenAI also publishes a short usage policy for the gpt-oss models.