Prompt Engineering vs Loop Engineering vs Graph Engineering: What Changes at Each Layer

Prompt engineering, loop engineering, and graph engineering are three different layers of control in AI systems, not competing techniques. Prompt engineering controls a single model response with human involvement at each step, while loop engineering automates a cycle where an agent observes, acts, and verifies without human intervention between steps. Graph engineering sits above both, controlling how multiple agents are organized and coordinated together, with routing rules determining retries and failures in advance. Each layer builds on the previous one without replacing it, addressing different problems: prompt engineering breaks down when tasks are high-volume or multi-step with no human available to evaluate outputs, while loop engineering cannot distinguish between completion and being stuck, and graph engineering handles cross-domain work with parallel branches.