Route by consequence
Use fast, economical models for classification, first-pass questions, formatting and routine transformations. Reserve frontier reasoning models for architecture, ambiguous trade-offs, long-context synthesis and final quality review.
The cheapest failed run is still expensive
Token price is only one cost. Rework, missing requirements and an unreliable implementation can consume more time than a careful planning pass. The goal is not the lowest price per request; it is the lowest reliable cost per accepted outcome.
Keep routing observable
Record which provider and model produced a saved checkpoint. Test structured-output and research requirements before changing a production route. A model name alone does not prove compatibility with your workflow.