Latent Space / OpenAI: Harness Engineering — 3 Engineers Ship 1M LOC with Zero Human-Written Code via 'Dark Factory'

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Ryan Lopopolo (OpenAI Frontier) revealed on the Latent Space podcast how his team of 3 engineers built Symphony — OpenAI's internal orchestration layer — as a 1M+ line Elixir codebase with zero human-written code and zero pre-merge human review, burning >1B tokens/day (~$2-3K/day). Key patterns include 1-minute max build loops, 5-10 PRs per engineer per day, 'ghost libraries' (software distributed as specs agents implement independently), post-merge review instead of pre-merge, and 6 markdown skill files as guardrails. OpenAI published a companion blog post coining the term 'Harness Engineering' — designing constraints, tools, and verification systems for AI agents rather than writing code yourself.