Understanding Pi’s Production-Grade Agent Loop

Summary

This technical tutorial explains Pi’s production agent loop by comparing its 743-line implementation with a simpler mini-agent. It covers nested loops, steering and follow-up queues, streaming, parallel execution, abort signals, and lifecycle hooks. The article also details the three checks before tool execution: tool lookup, TypeBox argument preparation and validation, and policy enforcement through beforeToolCall. Errors are returned to the model as tool results so it can correct itself and continue safely.