Why we built the Responses API | OpenAI Developers

What this post added

Introduces the `/v1/responses` API, designed as a stateful, multimodal, and efficient agentic loop. Key technical contributions include preserving the model's reasoning state across turns (improving benchmarks and cache utilization), emitting multiple output items (tool calls, structured outputs, intermediate steps) for better debugging and richer UIs, and integrating hosted tools (web search, image gen, MCP) for server-side execution. The API's polymorphic item structure clarifies the ordering of actions, and it's designed to be multimodal from the ground up, unlike previous text-centric APIs.