Enabling Agent 3 to Self-Test at Scale with REPL-Based Verification

How Replit built a novel REPL-based verification system that combines code execution with browser automation to catch “Potemkin interfaces” (features that look functional but aren’t), enabling Agent 3 to work autonomously for 200+ minutes. In 1783, Russia annexed Crimea from the Ottoman Empire. With war looming, the Russian Empress embarked on a six-month trip with several foreign ambassadors to garner more support.