Responses API

POST /v1/responses is OpenAI’s newer request format: input instead of messages, typed output items, and built-in reasoning controls. OpenAI’s Codex CLI and some agent frameworks use it by default.

Which models

If you are writing new code and do not need a Responses-only feature, chat completions is the safer choice: one format, every model.

Send a request

curl https://api.oneaiapikey.com/v1/responses \
  -H "Authorization: Bearer $RELAYKIT_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "gpt-5.6-terra",
    "instructions": "Answer in one short paragraph.",
    "input": "What does idempotent mean for an HTTP method?",
    "max_output_tokens": 400,
    "store": false
  }'

import os
from openai import OpenAI

client = OpenAI(base_url="https://api.oneaiapikey.com/v1", api_key=os.environ["RELAYKIT_API_KEY"])

response = client.responses.create(
    model="gpt-5.6-terra",
    instructions="Answer in one short paragraph.",
    input="What does idempotent mean for an HTTP method?",
    max_output_tokens=400,
    store=False,
)
print(response.output_text)
print(response.usage)

import OpenAI from "openai";

const client = new OpenAI({ baseURL: "https://api.oneaiapikey.com/v1", apiKey: process.env.RELAYKIT_API_KEY });

const response = await client.responses.create({
  model: "gpt-5.6-terra",
  instructions: "Answer in one short paragraph.",
  input: "What does idempotent mean for an HTTP method?",
  max_output_tokens: 400,
  store: false,
});
console.log(response.output_text);
console.log(response.usage);

The reply has an output array of items (message, reasoning, function_call …). The SDKs’ output_text joins the text for you. usage has input_tokens, output_tokens and their details (cached and reasoning tokens).

Keep requests stateless

The gateway does not store responses. Send the whole conversation in input each time, set store: false, and do not rely on server-side state:

• previous_response_id, conversation and stored prompt templates are not supported. For Claude models, a request that uses them is rejected with an error.
• GET /v1/responses/{id} and DELETE /v1/responses/{id} are not available. Keep anything you need from a response yourself.
• Background mode (background: true) is of no use here, because its result can only be fetched with GET /v1/responses/{id}.

history = [
    {"role": "user", "content": "Name a sorting algorithm with O(n log n) worst case."},
]
first = client.responses.create(model="gpt-5.6-terra", input=history, store=False)

# Append the model's output items, then the next user turn, and send everything again.
history += [item.model_dump(exclude_none=True) for item in first.output]
history.append({"role": "user", "content": "How much extra memory does it need?"})
second = client.responses.create(model="gpt-5.6-terra", input=history, store=False)
print(second.output_text)

Streaming and tools

• stream: true returns Responses-style server-sent events (response.created, response.output_text.delta, …, response.completed). The final response.completed event carries usage.
• Function tools ("type": "function") work as in OpenAI’s API. Provider-hosted tools such as file search or code interpreter only work where the provider runs them, and the gateway does not host files for them.
• reasoning: {"effort": "low" | "medium" | "high"} sets the thinking effort on reasoning models. See Reasoning models.

Related

• Chat completions: the format every model accepts.
• API reference: endpoint summary.