The economics of AI APIs are shifting. Developers building production applications with the OpenAI SDK can now point that same SDK at DeepSeek's API, access capable models, and pay substantially less per token. This tutorial walks through a working provider-agnostic AI client, a streaming implementation, and a full-stack React plus Node.js chat application backed by DeepSeek, with production-ready error handling and a deployment checklist. How to Use the DeepSeek API with the OpenAI SDK Install the OpenAI Node.js SDK ( openai@^4.x ) and project dependencies ( express , cors , dotenv ). Generate a DeepSeek API key from platform.deepseek.com and store it in a .env file. Configure the OpenAI client constructor with DeepSeek's baseURL ( https://api.deepseek.com ) and your DeepSeek API key. Set the model parameter to deepseek-chat (general-purpose) or deepseek-reasoner (chain-of-thought). Abstract the provider choice into a provider-agnostic client module driven by environment variables.…