No fancy infrastructure. Just a 50-line Python function that picks the right model for the right query. Last month my LLM API bill hit $340. This month: $67. Same traffic. Same product. The only change was adding a simple router that stops sending every request to Claude Sonnet when GPT-4o mini can handle it just as well. Here's exactly how it works. The Problem When you prototype, you pick one model and hardcode it everywhere. Usually something capable like GPT-4o or Claude Sonnet,...