Model Routing: 3 Things I Learned Sending Tasks to the Cheapest Model That Actually Works

Everyone benchmarks models. Sonnet beats Haiku on reasoning. Opus beats Sonnet. Haiku is fastest. These things are all true. But benchmarking and deploying are different games. At scale, the difference between Haiku at $0.80/million tokens and Sonnet at $3/million tokens isn't academic. It's $400+ monthly on a mid-size application. The trap is paying for capability you don't actually need because you never measured what you do need. I built a router to answer one question: which tasks in my actu