Responses API and Agents SDK
OpenAI also has a newer Responses API and an Agents SDK for JS. They build on the same ideas as chat completions.
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Analogy
Like learning fetch before axios. Once you know the raw call, the nicer wrapper is just less typing.
In an agent
Learn chat completions first; that knowledge transfers directly to the newer APIs and to every agent framework.
Questions people ask
What is the OpenAI Responses API?
It is a newer OpenAI API for building assistants and agents, alongside an Agents SDK for JavaScript. It builds on the same ideas as chat completions: messages, tools and structured output. If you understand chat completions, you already understand most of it; it mainly saves you some of the bookkeeping.
Should I learn chat completions or the Responses API first?
Start with chat completions. It is the most widely used shape, almost every framework and tutorial builds on it, and it shows clearly what an agent does on each step. Once you know it, moving to the Responses API or the Agents SDK is mostly learning a nicer wrapper.