Protocols

Anthropic-compatible API

Claude clients speak the Anthropic Messages API, and so does RelayRouter. Point the Anthropic SDK at https://relayrouter.io, keep the request shape, the anthropic-version header and the streaming events exactly as they are, and swap in a RelayRouter key. Claude Code works the same way through two environment variables.

Base URL and endpoints

https://relayrouter.io No /v1 suffix: the Anthropic SDK and Claude Code append /v1/messages themselves.

Authentication: x-api-key: <your RelayRouter key>, or Authorization: Bearer <key>. Both headers are accepted; keep anthropic-version as your SDK sends it.

Code

import anthropic

client = anthropic.Anthropic(
    api_key="your-relayrouter-key",
    base_url="https://relayrouter.io",
)

msg = client.messages.create(
    model="claude-opus-5-5",
    max_tokens=1024,
    messages=[{"role": "user", "content": "Hello!"}],
)
print(msg.content[0].text)

import Anthropic from "@anthropic-ai/sdk";

const client = new Anthropic({
  apiKey: process.env.RELAYROUTER_API_KEY,
  baseURL: "https://relayrouter.io",
});

const msg = await client.messages.create({
  model: "claude-sonnet-4-6",
  max_tokens: 1024,
  messages: [{ role: "user", content: "Hello!" }],
});
console.log(msg.content[0].type === "text" ? msg.content[0].text : "");

export ANTHROPIC_BASE_URL="https://relayrouter.io"
export ANTHROPIC_AUTH_TOKEN="your-relayrouter-key"
export ANTHROPIC_MODEL="claude-opus-5-5"
claude

Groups that speak this protocol

A key belongs to one group. Create it in the console for one of the groups below; the models page has every group and model with live rates.

Tools that work as-is

• Anthropic SDK (Python, TypeScript, Java, Go): set base_url and api_key
• Claude Code: ANTHROPIC_BASE_URL and ANTHROPIC_AUTH_TOKEN (guide)
• Cline / Roo Code: Anthropic provider with a custom base URL (guide)
• LangChain ChatAnthropic: anthropic_api_url=https://relayrouter.io

Questions