Use the OpenAI SDK

1. Install the SDK: pip install openai (Python) or npm i openai (Node.js)
2. Set base_url to https://api.onefast.ai/v1
3. Set api_key to your key
4. Call client.chat.completions.create(model=...) — fill in any model ID

> The whole OpenAI ecosystem (LangChain, LlamaIndex, Dify, FastGPT, OneAPI) works the same way.