Stop building reactive agents: Why your architecture needs a System 1 and System 2

If you’ve built an LLM agent recently, you’ve probably hit the "autonomy wall." You give the agent a tool to search the web, a prompt to "be helpful," and a task. For the first two turns, it looks like magic. On turn three, it goes down a Wikipedia rabbit hole. On turn ten, it’s stuck in an infinite loop trying to fix a syntax error on a file it never downloaded. Most developers try to fix this by cramming more instructions into the system prompt: "Never repeat the same action twice! Think step-by-step!" But the problem isn’t the prompt. It’s the architecture. You are forcing a single execution loop to do two completely different jobs: talking/acting (which requires low latency and high bandwidth) and planning (which requires slow, deliberative reasoning). We need to borrow a concept from human psychology—Daniel Kahneman’s Thinking, Fast and Slow —and build Dual-Process Agents . The Problem: The Single-Loop Trap Most standard agents (like a naive ReAct loop) operate in a flat sequence: