OpenAI API

The OpenAI API provides programmatic access to GPT-4, GPT-3.5, DALL-E, Whisper, and other models that have redefined what's possible with AI. If you're building products that use AI for text generation, code completion, image creation, or speech recognition, this is where most teams start. GPT-4 is the flagship text model. It handles complex reasoning, follows nuanced instructions, and produces coherent long-form content. The context window extends to 128k tokens, meaning you can include substantial documents or conversation history. For many applications, GPT-4 is simply the most capable option available. The chat completions API is the primary interface. You send a conversation—a sequence of messages with roles—and receive a response. System prompts establish behavior, function calling enables tool use, and streaming returns partial responses in real-time for better UX. Embeddings power semantic search and similarity. Convert text to vectors, store in a vector database, and find relevant content without keyword matching. This enables RAG (retrieval-augmented generation), where GPT answers questions based on your specific data. Fine-tuning lets you customize models on your data. While GPT-4 isn't fine-tunable, GPT-3.5 can be trained to match your style, terminology, or specific task requirements. The fine-tuning API handles the training; you provide examples. Pricing is usage-based on tokens processed. GPT-4 costs significantly more than GPT-3.5, so many applications use GPT-3.5 for simple tasks and escalate to GPT-4 when needed. For high-volume applications, understanding costs is important. The developer experience is excellent. SDKs exist for every major language, documentation is comprehensive, and the playground helps prototype prompts before coding.