Latent Space: The AI Engineer Podcast

Extreme Harness Engineering for Token Billionaires: 1M LOC, 1B toks/day, 0% human code, 0% human review — Ryan Lopopolo, OpenAI Frontier & Symphony

2068 snips
Apr 7, 2026
Ryan Lopopolo, an OpenAI engineer building enterprise-scale agent systems, talks about harness engineering, running a 1M+ LOC codebase with no human-written or reviewed code, and spending billions of tokens a day. They get into Symphony, multi-agent orchestration, one-minute build loops, agent-led code review, and why teams should optimize for agent legibility over human coding habits.
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Zero Human Code Started Painfully Slow

  • Ryan Lopopolo started with early Codex CLI and deliberately refused to write code himself, forcing the agent to do the job end to end.
  • The first month and a half was 10x slower, but decomposition plus better primitives turned it into a system faster than any one engineer.

Keep Agent Build Loops Under One Minute

  • Keep the inner build loop under a minute and treat any overrun as a signal to stop and decompose the build graph.
  • Ryan Lopopolo retooled from Make to Bazel to Turbo to NX in a week because fast builds mattered more than human preferences.

Human Attention Became The Real Bottleneck

  • Human attention became the scarce resource, not tokens, so the team stopped centering review around reading every PR.
  • They shifted effort into observability, modular primitives, and confidence-building automation so agents could review, fix, and merge autonomously.
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