How to Use Multiple LLMs With OpenRouter

How do you use multiple LLMs with OpenRouter?

You use multiple LLMs through OpenRouter by sending all your requests to a single OpenRouter endpoint with one API key, and choosing which model runs each request by name. OpenRouter is a unified gateway that sits in front of many providers — OpenAI, Anthropic, Google, Meta's open models, and more — and exposes them through one consistent, OpenAI-compatible API. Instead of managing a separate account, key, and SDK for every provider, you integrate once and switch models by changing a single string in the request.

Because the interface follows the OpenAI Chat Completions shape, the official OpenAI SDK works against OpenRouter with only the base URL and key swapped, so adopting it rarely means rewriting your calls. If you already have working OpenAI code, pointing it at OpenRouter is close to a configuration change rather than a migration, which is a large part of why teams reach for it when they want to experiment across models without committing engineering time to each new provider one at a time.

What you get from a single gateway

• One integration, many models — access dozens of models from different providers without wiring up each API separately.
• Trivial model switching — compare a small model against a flagship, or move to a newer release, by editing the model name.
• One bill and one key — consolidated billing and credentials instead of scattered accounts.
• Access to open models — hosted open-weight models sit alongside the big commercial APIs under the same interface.

The real value is optionality. When a better or cheaper model ships, you can try it in minutes instead of building a new integration first.

Route the right task to the right model

With many models a request away, you can stop paying flagship prices for simple work.

1. Send routine jobs — classification, short replies, extraction — to a small, cheap model.
2. Route hard reasoning to a stronger model only when the task needs it.
3. Experiment freely: because switching is just a name change, you can A/B different models against your real prompts and measure quality, latency, and cost.

This per-task routing is the same strategy that controls cost on a single provider, except OpenRouter lets the candidates come from across the whole market.

Build in fallbacks for resilience

A single-provider integration goes down when that provider does. Routing through a gateway lets you fail over. OpenRouter supports specifying fallback models, so if your first choice is unavailable or rate-limited, the request can be served by an alternative instead of erroring out. For a production feature that users depend on, that automatic resilience is worth designing in — an outage at one lab becomes a transparent switch to another rather than a broken feature.

Weigh the trade-offs honestly

A gateway adds convenience and a layer of dependency, so go in clear-eyed.

• An extra hop — your traffic passes through OpenRouter, adding a small amount of latency and a third party to your data path.
• Pricing — compare the gateway's rates against going direct; the convenience may carry a margin, which can still be worth it for the flexibility.
• Data handling — understand how the gateway and the underlying providers treat your data, especially for sensitive workloads.
• Newest features — a provider's very latest capability sometimes lands in their own API before it is exposed through a gateway.

For many teams the flexibility and simpler integration outweigh these costs, particularly early on when you are still deciding which models suit your product. If you later standardise on one model, you can always integrate it directly.

How to adopt it without regret

If you decide a gateway fits, a little structure keeps you in control rather than at its mercy.

• Keep your own thin abstraction — call the gateway through a small internal interface so you could swap to a direct provider later without touching feature code.
• Pin models explicitly — name the exact model each task uses rather than relying on a vague default, so behaviour does not shift under you.
• Track cost per model — log which model served each request and what it cost, so your routing decisions are driven by data.
• Test fallbacks deliberately — confirm your failover actually triggers, because an untested fallback is just a hope.

Done this way, a gateway gives you the breadth of the whole model market behind one integration, while your own abstraction keeps the exit door open. That combination — wide choice now, no lock-in later — is exactly what you want while the landscape is still moving this fast.

Prefer it built for you?

A multi-model setup with smart routing and fallbacks is a strong foundation, but getting the routing logic, cost controls, and data handling right takes care. Talk to BSH Technologies about our software engineering services and we will design a resilient, cost-aware multi-LLM architecture for your product.