Here’s a confession that’ll probably get me kicked out of the AI engineering community: I spent three months selecting an LLM based on benchmark scores, built an entire production system around it, and watched it fail spectacularly in ways no benchmark predicted. The model scored 94% on reasoning tasks. It couldn’t handle a simple user asking “wait, what did I just say?” without losing its mind.
Let me tell you why everything you think you know about choosing an LLM is probably wrong, and more importantly, what metrics actually matter when your system is bleeding money because your chosen model decided to hallucinate pricing information to paying customers.