5 Architecture Mistakes We Made Building 200 Production AI Systems

After building 200+ production AI systems, we've made every mistake possible. Here are the 5 that cost our clients the most money - and what we do instead now. 1. Using a Single LLM for Everything Our first 20 projects used one model (GPT-4) for everything: classification, generation, extraction, analysis. The cost was brutal - $2,000+/month for a single client's chatbot. What we do now: Route queries to the cheapest model that can handle them. Simple classification → GPT-4o-mini ($0.15/1M tokens). Complex reasoning → Claude Opus ($15/1M tokens.