Long-running agents fail at step 95 of 100: system design is back

arpit_bhayani · x · 2026-11-12

Arpit Bhayani pushes back on the claim that system design no longer matters, arguing long-running agents will make it essential again.

He splits agentic apps into two classes: short-running agents can survive with a simple retry loop since each LLM call is isolated, cheap, and stateless. Long-running agents spanning hours are different — retries are costly in API spend, side effects (e.g. duplicate notifications), and wall clock time.

Common production failures he lists: LLM provider rate limits, network timeouts, OOM-killed pod evictions mid-run, pod rotation during deploys, context window overflow, and human-in-the-loop pauses lasting days.

His key point: most of these aren't AI problems — they're classic software engineering problems reappearing in a new system. The solutions are backend fundamentals: checkpointing, idempotency, durable event logs, and resumable workflows.

Takeaway: abstractions change, fundamentals don't. Eventually you ship your "tutorial" to production.

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