Is Multi-Provider LLM Routing Worth the Added Complexity, We Tested It

Multi-provider routing — sending easy tasks to a cheap model and hard tasks to an expensive one, dynamically, across vendors — is one of those ideas that sounds obviously correct in a planning meeting. We built it for a client with genuinely high volume and mixed task difficulty, and the result was a useful lesson in where the idea actually pays off.

What it cost to build

A routing layer needs a classifier to decide task difficulty, consistent prompt templates across providers with different quirks, per-provider error handling and retry logic, and a way to track quality drift separately for each provider, since 'the model' is now plural and each half can silently degrade independently. That's a real system, not a config flag.

Multi-provider routing isn't a feature you add, it's a second system you now own and have to keep healthy alongside the first one.

Where it paid off and where it didn't

• At genuinely high volume with a clear easy/hard task split, routing cut costs by around 30% — the case it's built for.
• On a lower-volume project we tried it on next, the complexity overhead (maintenance, two providers' worth of incident response, double the eval surface) cost more engineering time than the savings were worth.
• The classifier itself became a maintenance burden — it needed retraining as task distribution shifted, which is its own small ML project nested inside the routing project.

My actual rule now: multi-provider routing is worth it when volume is high enough that the savings are a real line item on a budget, and the task mix is stable enough that the classifier doesn't need constant babysitting. Below that bar, it's complexity you're buying for savings you won't notice, and a single well-chosen provider with good prompt engineering gets you most of the benefit for a fraction of the maintenance.