What is a request fan-out architecture in classification systems?

Request fan-out architecture sends a single request to multiple services or models in parallel and aggregates the results.

In complex classification systems, fan-out is used when a decision depends on multiple models or feature sources. A single request is decomposed into parallel calls to feature stores, embedding services, or specialized classifiers. The results are then merged using aggregation logic like weighted voting or stacking. While it improves flexibility and model richness, it introduces challenges such as increased tail latency (p99), partial failures, and inconsistent responses. Systems often use timeouts, circuit breakers, and fallback strategies to manage these risks.