API integration is how AI capabilities get embedded into products: instead of interacting with a model through a chat interface, a product sends requests to the model’s API — a standardized programming interface — and incorporates the responses into its own user experience. Almost all commercial AI model access happens this way, through providers like Anthropic, OpenAI, or Google. For behavior architects, understanding API integration matters because product-level system prompts, model version pinning, temperature settings, and safety parameters are all configured at the API level. Design choices made in API integration — which model version to use, how to structure the system prompt, whether to use streaming — have direct behavioral implications.