The OpenAI API provides programmatic access to cutting-edge large language models (LLMs) including GPT-4, GPT-5, and specialized models for text generation, embeddings, image creation, speech processing, and moderation. Launched as a RESTful API with official SDKs for Python, Node.js, and other languages, it enables developers to integrate AI capabilities into applications via simple HTTP requests. Unlike the ChatGPT web interface (a consumer product), the API offers token-based pricing, fine-grained control over model parameters, and no rate limits for paid tiers — making it the foundation for production AI applications ranging from chatbots to code generation tools. In 2026, OpenAI introduced the Responses API as the successor to Chat Completions, offering better performance with reasoning models and streamlined tool usage, while deprecating the older Assistants API (shutdown scheduled for August 26, 2026). Key to effective API usage is understanding prompt caching (which can reduce costs by up to 90%), structured outputs for guaranteed JSON schema adherence, and function calling for connecting LLMs to external tools and databases.

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