Definition
Designing the feedback cycles around an agent so action, verification, operational triggers, and system improvement have explicit state, evidence, limits, and stopping conditions. LangChain's proposed taxonomy nests four levels: a core agent loop does work, a verification loop checks an attempted result, an event-driven workflow connects the agent to an operating system, and an outer improvement loop changes the harness using evidence from prior runs.
The useful insight is not the number four. It is that each loop has a different job and therefore needs a different completion rule, authority boundary, cost budget, and evidence standard. The outer loop should improve the inner loops without sharing their authority or changing their evidence.
Distinguish it from nearby terms
An agent loop is the local model-and-tool cycle. Loop engineering covers the surrounding feedback system. Graph engineering makes nodes, state, and transitions explicit; a loop is a cyclic graph, so the two terms describe overlapping views rather than competing architectures.
Check your understanding
For every loop, identify what changes, what evidence sends work around again, what stops it, and which outer control can refuse promotion.