I'm Sorry, but You Still Have to Think

It's all about the bit · 1 week ago · 43

A write-up by Piotr Sarnacki describes DHH using an AI agent to rewrite Campfire from Ruby on Rails to Rust (and later Elixir and Go) without directly writing or reading the code. The Rust version delivered only 1% of new post notifications under heavy load (reported as 1% out of 6–7k events), and later tuning a broadcast stream capacity from 256 to 16384 increased delivery to ~90% while raising pMAX latency from 11s to over 130s. The results show that vague prompts and benchmark-only evaluation lead to incorrect trade-offs and failure modes, so developers still need to read, test, and set constraints rather than assume the rewrite will “just work.”