Loop Engineering: The Layer After Prompt, Context, and Harness Engineering

A few weeks ago, I read a line from Boris Cherny, the person behind Claude Code, that stuck with me. He said he does not prompt Claude anymore. He has loops running, and those loops are the ones prompting Claude and deciding what to do next.

I sat with that for a while. For two years, every guide on working with AI agents told us to get better at writing instructions. Then it told us to get better at feeding the model the right information. Then it told us to build proper scaffolding around the agent so that it behaves like trustworthy software. Now there is a fourth layer, and it is less about talking to the agent and more about building a small system that talks to the agent for you. People are calling it loop engineering.