Most LLM APIs I review have one IChatClient and a prayer. Hello goes to the same model as "why does this async code deadlock under load." When that provider returns 503 for twenty minutes, so does the product. Routing and failover both matter. Mixing them up is how you get a green uptime chart and worse answers. The full sample (Microsoft.Extensions.AI routing types, circuit breaker, tests, offline profile) is in Tech Skill Builder . Here is the short version: a few hard rules, then a Q&am...