How to route between models with OpenRouter

Managing multiple LLM providers means multiple API keys, multiple SDKs, different rate limits, and different pricing. OpenRouter unifies all of them behind a single OpenAI-compatible API endpoint. One key, one SDK, access to GPT-4o, Claude, Gemini, Llama, Mistral, DeepSeek, and hundreds more.

OpenRouter also adds a routing layer: you can set fallbacks so if Claude is unavailable, requests automatically route to GPT-4o; or use cost routing to automatically select the cheapest model that meets your quality requirement.

Create an account at openrouter.ai. Add credits (minimum $5) and generate an API key. Set it as `OPENROUTER_API_KEY` in your environment.

OpenRouter is fully OpenAI API-compatible. Use the OpenAI SDK with a custom base URL: Python: `client = OpenAI(base_url='https://openrouter.ai/api/v1', api_key=os.environ['OPENROUTER_API_KEY'])`. Node: `const client = new OpenAI({baseURL: 'https://openrouter.ai/api/v1', apiKey: process.env.OPENROUTER_API_KEY})`.

Model IDs on OpenRouter follow the format `provider/model-name`. Examples: `anthropic/claude-sonnet-4-5`, `openai/gpt-4o`, `meta-llama/llama-3.3-70b-instruct`, `deepseek/deepseek-r1`, `google/gemini-2.5-flash`.

The OpenRouter model list at openrouter.ai/models shows pricing, context length, and benchmarks for every available model. Filter by price, context window, or provider to find the right model for your use case.

Use `openai/auto` as the model to let OpenRouter automatically select the cheapest model that can handle your request. Add a `route` header to specify preferences: `{'HTTP-Referer': 'your-app', 'X-Title': 'your-app', 'route': 'cheapest'}`.

For tasks where quality varies a lot by model, use the model ranking feature: pass a list of models in order of preference with a fallback option. OpenRouter tries the first model; if it is unavailable, it tries the next.