Latent Space · 2026-04-07 · major
Latent Space: Extreme Harness Engineering — 1M LOC, 1B Tokens/Day, 0% Human Code, 0% Human Review
OpenAI's Ryan Lopopolo recounts building a million-line internal product with zero human-written code using AI agents, revealing the Symphony orchestration system that handles the full PR lifecycle including review and merge.
OpenAI built a 1M-line product with zero human code — here's how the harness works.
What is it?
Latent Space deep-dive with OpenAI's Ryan Lopopolo on building a million-line internal product entirely by AI agents using Symphony, an orchestration system for autonomous PR lifecycle management.
How does it work?
Symphony agents handle spec writing, implementation, code review, and merge — with one-minute build loops as the forcing function that keeps agent iteration fast enough to be practical.
Why does it matter?
This is the most detailed public account of a team eliminating human code contribution entirely, with concrete engineering patterns replicable by any ambitious engineering team.