engines
Model router
The component that decides which LLM (and which retrieval pipeline) handles each query — invisible to the user but consequential for AEO.
Definition
A model router is the infrastructure that, given a user query, decides which model handles it: fast/cheap model for simple lookups, frontier model for complex reasoning, search-tool-enabled model for grounded answers. ChatGPT, Claude.ai, Perplexity, and Gemini all use model routers. Different routes = different retrieval pipelines = different citation patterns. Some routes never trigger a web fetch.
Example
ChatGPT may answer 'what's the capital of France' from training data (no citation), but 'what's Stripe's current pricing' from web tool (cited).How to optimize
Optimize for retrieval-enabled routes. Queries that mention current dates, prices, comparisons, or news typically route to the tool-enabled model — those are your AEO targets.