Your first request

Relay exposes an OpenAI-compatible Chat Completions API. Create a key, set the base URL, and send a message using any enabled model.

curl /v1/chat/completions \
  -H "Authorization: Bearer $RELAY_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"model":"gpt-5.5","messages":[{"role":"user","content":"Hello"}]}'

Authentication

Send your Relay API key in the Authorization header on every request. Keys are shown once when created; use a separate key for each environment and never expose one in browser code.

Authorization: Bearer $RELAY_API_KEY

Request format

Requests use JSON. model and messages are required; generation controls are optional.

Use the JavaScript SDK

Relay is compatible with the OpenAI SDK. Point the client at your Relay base URL and keep the API key on the server.

import OpenAI from "openai";

const client = new OpenAI({
  apiKey: process.env.RELAY_API_KEY,
  baseURL: "/v1"
});

const response = await client.chat.completions.create({
  model: "gpt-5.5",
  messages: [{ role: "user", content: "Hello" }]
});

console.log(response.choices[0].message.content);

Agent harnesses

Use Relay directly from coding agents. The gateway translates Anthropic Messages and native Gemini GenerateContent requests—including streaming, images, function calls, and tool results—into the same metered Relay model routes.

export ANTHROPIC_BASE_URL=""
export ANTHROPIC_AUTH_TOKEN="$RELAY_API_KEY"
export ANTHROPIC_MODEL="claude-opus-4-6"
export ANTHROPIC_SMALL_FAST_MODEL="claude-opus-4-6"
claude

export GEMINI_API_KEY="$RELAY_API_KEY"
export GOOGLE_GEMINI_BASE_URL=""
gemini -m gemini-3.5-flash

Streaming responses

Set stream to true to receive server-sent events. Read each data: frame in order and stop when the stream emits [DONE].

curl -N /v1/chat/completions \
  -H "Authorization: Bearer $RELAY_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"model":"gpt-5.5","messages":[{"role":"user","content":"Hello"}],"stream":true}'

Limits and reliability

Limits protect workspace credit and gateway availability. Read the response headers and use exponential backoff with jitter after a 429.

Errors

Relay returns standard HTTP status codes and a JSON error object with a human-readable message.

Choose a model

Use the exact model ID shown in the Models catalog. Pricing, context limits, and availability are shown there; the request format remains the same across providers.