gpt-oss-120b
gpt-oss-120b is an open-weight 117B-parameter Mixture-of-Experts model from OpenAI for high-reasoning, agentic and general-purpose production use. It activates 5.1B parameters per forward pass.
Pricing: Input 30 credits / 1M tokens (≈ $0.15), Output 120 credits / 1M tokens (≈ $0.60).
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gpt-oss-120b API on ModelFold
gpt-oss-120b is an open-weight 117B-parameter Mixture-of-Experts model from OpenAI for high-reasoning, agentic and general-purpose production use. It activates 5.1B parameters per forward pass. Try gpt-oss-120b in the ModelFold Playground, then call it from your own code through an OpenAI-compatible chat completions API.
What Is the gpt-oss-120b API
gpt-oss-120b at a glance
gpt-oss-120b is a chat model from OpenAI. It accepts text as input and returns text, with a context window of up to 131K tokens.
Use it without hosting anything
On ModelFold you call gpt-oss-120b with a single API key — no model weights to download and no inference servers to run. The same key also works for the other chat, image, video and audio models on ModelFold.
Core Capabilities of gpt-oss-120b
Up to 131K tokens of context
Keep long conversations, large documents and sizeable code in a single request, so the model can reason over the full material instead of fragments.
Function calling
gpt-oss-120b supports tool (function) calling: describe your functions in the request and the model returns structured calls your code can run — the basis for agents and integrations.
Adjustable reasoning effort
Choose a reasoning effort level (low, medium or high) per request to balance depth of thinking against speed and token usage.
Structured outputs
Ask for JSON that follows a schema (response_format), which makes extraction, classification and system integrations more reliable.
How to Use gpt-oss-120b on ModelFold
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Step 1: Try it in the Playground
Open the Playground at the top of this page, type a prompt and see how gpt-oss-120b responds before writing any code.
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Step 2: Create an API key
Sign in to ModelFold and create an API key in the console. Keep it secret and send it as a Bearer token.
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Step 3: Send a request
Call POST https://modelfold.ai/v1/chat/completions with "model": "gpt-oss-120b" and your messages. Existing OpenAI-compatible SDKs work by changing the base URL and key.
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Step 4: Ship and monitor
Integrate the response into your product and check token usage and spend for every call in the console logs.
What You Can Build with gpt-oss-120b
Analysis and complex reasoning
Work through research questions, data interpretation, planning and other problems that need careful step-by-step reasoning.
Autonomous agents
Build agents that plan multi-step tasks, call your tools and APIs, and keep working toward a goal across long sessions.
Tool-calling backends
Route requests, call functions and chain API calls as the worker model inside larger agent systems.
High-volume pipelines
Run classification, extraction, rewriting and batch jobs at scale where cost per request matters.
Frequently Asked Questions
What is gpt-oss-120b?⌄
gpt-oss-120b is an open-weight 117B-parameter Mixture-of-Experts model from OpenAI for high-reasoning, agentic and general-purpose production use. It activates 5.1B parameters per forward pass.
Which inputs does gpt-oss-120b support?⌄
gpt-oss-120b accepts text and returns text. Through ModelFold you send text messages; documents attached in the Playground are converted to text.
How long is the context window of gpt-oss-120b?⌄
Up to 131K tokens, shared between your input and the model’s output.
Does gpt-oss-120b support function calling?⌄
Yes. gpt-oss-120b supports tools / function calling through the standard tools parameter of the chat completions API.
How is gpt-oss-120b billed on ModelFold?⌄
Pay as you go by tokens: input and output tokens are charged at the per-million-token prices shown on this page. There is no monthly fee, and failed requests are not charged.
How do I call gpt-oss-120b through the API?⌄
Send a POST request to https://modelfold.ai/v1/chat/completions with "model": "gpt-oss-120b", using your ModelFold API key as the Bearer token.
| Input | 30 credits 1M tokens≈ $0.15 |
| Output | 120 credits 1M tokens≈ $0.60 |
Billed per token: input and output are priced separately, and thinking tokens count as output. The Playground charges exactly the same way.
Read API docs →AI Agents · Claude Code / Cursor / Trae →curl https://modelfold.ai/v1/chat/completions \
-H "Authorization: Bearer $MODELFOLD_API_KEY" \
-H "Content-Type: application/json" \
-d '{"model":"gpt-oss-120b","messages":[{"role":"user","content":"Hello"}]}'