Dan Luu says agents changed the cost of building, and most people still price it the old way

Luu says he built a regex engine, a ripgrep fork and a faster Rust build setup for his own use, each in what he calls "a low single-digit number of hours" of his time. He estimates the same work would have taken a year or more before agents. He credits the idea to Michael Malis, who works on pgrust, a Postgres rewrite that Luu says has already surfaced real Postgres bugs. Luu's explanation for why people don't try such projects is that they carry a "pre-agentic cost model".

He is open about the limits. He did a quick comparison instead of rigorous benchmarks, so the speedups are his own unbenchmarked reports. He also writes that each more capable model leaves him further from "it just works", because what a model can implement grows faster than what it can verify without handholding. He includes a dissent from Yossi Kreinin, who argues most people should build less with AI, since many problems have no clear pass/fail criteria for an agent loop to use.

Why it matters: The argument is about cost estimates, and the evidence is one practitioner's projects. Still, the verification gap he describes is the part to check against your own work before scoping something large.