What Is an LLM Router and How Do You Evaluate It? (EXPLAINED)
Hard production LLM question on routing, cascading, and router evaluation.
TL;DR — Quick Answer
A router classifies query difficulty/risk and selects a model (or cascade). Evaluate with cost-quality curves on a labeled set: measure win rate vs always-frontier, cost savings, and catastrophic misroutes on high-risk queries. Include override rules for safety-critical intents.
The Interview Question
Design and evaluate an LLM router that sends easy queries to a cheap model and hard queries to a frontier model.
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