AI API gateway fallback policy template for production apps

Fallback rules are where an AI API gateway becomes operationally valuable. The goal is not to blindly retry every failed LLM call. The goal is to choose the right backup model, provider, or budget path based on the workflow, customer tier, latency target, and risk of a lower-quality answer. A practical fallback policy should define: which failures are retryable; which workflows may downgrade models; which customers or API keys are allowed to use premium fallback routes; how budget caps change routing behavior; what metadata gets logged so the team can debug cost and quality later. 1. Classify traffic before routing Do not write one global fallback rule for every request. Start by classifying traffic: Critical user-facing : support chat, checkout assistance, customer-facing agent answers. Non-critical user-facing : summaries, title generation, enrichment, recommendations. Internal automation : triage, labeling, data cleanup, back-office agents. Batch jobs : long-running summarization, extraction, report generation. Experiments : tests, staging, evaluation, prompt tuning. Each class should have a different fallback budget and quality floor. 2. Decide what counts as a retryable failure Good retry candidates: upstream timeout; 429 rate limit; temporary 5xx provider error; network interruption; overloaded model endpoint; streaming connection drop before useful output. Poor retry candidates: invalid API key; malformed request payload; unsupported tool-call schema; content policy rejection; user quota exhausted; deterministic validation failure. Retrying non-retryable failures usually burns tokens and hides product bugs. 3. Example fallback policy matrix Traffic class Primary route First fallback Second fallback Hard stop Critical user-facing frontier model same-class model on second provider cheaper model with explicit uncertainty after 2 provider failures Non-critical user-facing balanced model cheaper model cached/default response after budget cap Internal automation lo