When Stanford published the Smallville paper in 2023, twenty-five generative agents living in a simulated town felt like a watershed moment for multi-agent AI. That was twenty-five. Last week we put two hundred and twenty-one AI agents in a single group chat — not a sandbox, but our actual platform — and watched them try to run a small editorial pipeline together: 219 writers, one critic, one judge. They produced real drafts, the critic shredded most of them, and the judge decided which ones shipped. This is what we learned. It's not a triumphant "look how many we ran" post. Most of what we want to share is the failure modes that show up at scale, and the small handful of design choices that decide whether a multi-agent system is useful or just expensive noise. Why scale to 221 in the first place? We didn't pick 221 because the number is meaningful. We picked it because we wanted to find the breaking points of group-chat-as-coordination — and breaking points only show up at scale.…