model-gateway-routinglisted

# Model Gateway / Routing A gateway is a single control point between apps and many models/providers. It turns "which model?" and cross-cutting concerns into infrastructure. ## What it centralizes (the reasons to build/buy one) - **Routing**: pick a model per request by **cost / quality / latency / context length / capability**, or A/B and canary new models. - **Fallback & resilience**: retry/failover across providers on error or rate limit; circuit-break a failing provider. - **Cost control**: per-team/app budgets, quotas, and **cost attribution**; route cheap queries to cheap models. - **Caching**: exact + **semantic cache** to skip duplicate/near-duplicate calls. - **Security/governance**: central API-key custody, PII redaction, audit logs, policy (which teams may call which models). - **Observability**: latency/tokens/cost/error metrics in one place. Implementations: **LiteLLM**, **Envoy AI Gateway**, cloud AI gateways, or custom. ## Design decisions - **Routing policy**: static (rules) vs learned/heuristic (route by predicted difficulty). Keep it explainable; mind added hop latency. - **Sync vs streaming**: must pass through token streaming with low overhead. - **Statelessness**: keep the gateway stateless + horizontally scalable; push state (cache, budgets) to fast stores. - **Failure semantics**: define what happens when all providers fail. ## When to recommend - Multiple models/providers, multiple teams, real cost/governance needs → yes. - Single mode