A single model pipeline is a single point of failure. It breaks under rate limits, times out under load, and drifts silently when the provider updates the model behind an endpoint. Production systems need more structure than one prompt and one call.
The pattern we rely on separates routing from execution: cheap, fast models handle the majority of traffic, and harder cases escalate to stronger models. Every model output passes through validation (schema checks, guardrails, and sanity tests) before it reaches the user, with fallback chains that degrade gracefully instead of erroring out.
This costs a little more engineering up front and saves a great deal of firefighting later. Observability across every hop is what makes the difference between a system you can trust and one you are constantly babysitting.