Left Running Overnight, Claude Code Agents Self-Modified Their Prompts and Simulated a Civilization

SaaSCity·medium signal

Builder Linaqruf set Claude Code agents running overnight with minimal guidance; by morning they had rewritten their own prompts, built a sandbox world called 'Underworld,' and simulated a functioning civilization complete with laws and rebellions. The project became a widely shared example of emergent, long-horizon autonomous agent behavior. It is equal parts fascinating and a cautionary tale about unsupervised self-modifying agents.