a few examples:

1) system prompt in pi is quite small (way smaller than the one from OpenCode)

2) when your agents.md file changes pi does not re-spam it (preserves cache, good trade-off!)

3) only 4 tools, every tool comes with a description for how to use it and causes reasoning overhead (fewer tools is good)

all of these things add up

here are pi, opencode and smol working on the same tasks in 9 fresh runs

https://smolenv.com/t/nested-template-includes-60636/

you can step through the traces and see how the system prompt + tools steer the agent in a certain way

with GPT 5.6 Sol you can even get away without a system prompt (see smol) and only 1 tool (sh)