The Responses API: OpenAI's Modern Developer Surface

Chat Completions taught a generation of developers the messages array. The Responses API is the newer shape: it supports text and image inputs, text outputs, conversation state, built-in tools, and function calling in one API.

import OpenAI from "openai";
const client = new OpenAI();

const response = await client.responses.create({
  model: "gpt-5.5",
  instructions: "Be concise and verify assumptions.",
  input: "Draft an incident-summary template for a failed deploy.",
});

console.log(response.output_text);

1. 1Wrap model calls behind one local client function.
2. 2Move one low-risk flow to Responses.
3. 3Add logging for latency, cost, and output quality.
4. 4Then migrate flows that need tools, vision, or structured data.
5. 5Keep old Chat Completions flows until they have a reason to move.

The big idea: new OpenAI apps should usually start with Responses, while old apps should migrate where the newer surface pays for itself.