OpenAI Compatibility

When to Use This Route

• Use the OpenAI-compatible route with a Basic key for Claude models, or with a Codex key for OpenAI/GPT models.
• Use the native /v1/messages route if you want the most Claude-native behavior, cleaner troubleshooting, or direct Anthropic-style SDK integration.
• For Cursor, Cline, Roo Code, and similar OpenAI-style tools, choose the key group that matches the model family. Kilo Code has a separate OpenAI Responses provider for GPT/Codex models; see the Kilo Code guide.

Endpoint

Authentication

Use the standard Authorization: Bearer header with your LLMsRelay API key:

curl https://api.llmsrelay.com/v1/chat/completions \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "content-type: application/json" \
  -d '{
    "model": "claude-sonnet-4.6",
    "messages": [{"role": "user", "content": "Hello!"}]
  }'

Python (OpenAI SDK)

from openai import OpenAI

client = OpenAI(
    api_key="YOUR_API_KEY",
    base_url="https://api.llmsrelay.com/v1"
)

response = client.chat.completions.create(
    model="claude-sonnet-4.6",
    messages=[
        {"role": "system", "content": "You are a helpful assistant."},
        {"role": "user", "content": "What is machine learning?"}
    ]
)

print(response.choices[0].message.content)

TypeScript (OpenAI SDK)

import OpenAI from "openai";

const client = new OpenAI({
  apiKey: "YOUR_API_KEY",
  baseURL: "https://api.llmsrelay.com/v1",
});

const response = await client.chat.completions.create({
  model: "claude-sonnet-4.6",
  messages: [{ role: "user", content: "Hello!" }],
});

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

Important Compatibility Notes

• Use Authorization: Bearer YOUR_API_KEY and the /v1 suffix. This route is not the same as the native Anthropic-format endpoint.
• System and developer instructions may be treated as one combined top-level instruction rather than as fully independent turns.
• OpenAI-specific fields that are not part of Claude's native behavior may be ignored. Do not assume every OpenAI-only knob changes model behavior.
• For tool calling, you should not rely on strict schema guarantees just because your OpenAI client exposes a strict mode toggle.
• If a feature feels awkward to express through Chat Completions, switch to the native /v1/messages API instead of fighting the compatibility layer.