The 4 layers of an agent system: failures are often architecture problems, not prompting problems
blaizedsouza · x · 2026-09-06
A thread arguing that when an agent burns tokens, declares completion and then fails tests, it's usually an architecture problem around the model — not a prompting problem — and rewriting prompts or switching models won't fix it.
The author breaks agent systems into four layers:
- Loop: the smallest unit of agency — act, check, then stop or retry. The key is how completion is decided: a reliable agent shouldn't stop just because the model believes the work looks correct, but when external evidence exists (passing tests, successful builds, validated outputs or other measurable conditions)
- Without this verification loop, an agent can declare victory prematurely
- The full thread is truncated, but the core thesis stands: different failures must be solved at different layers
Practical takeaway for agent builders: build the verification loop for "what counts as done" before tweaking prompts or models.
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