Replit rebuilt its sandbox engine with microVMs

Replit has completed a major rebuild of its sandbox engine, replacing its Docker-based infrastructure with microVMs to improve security, capabilities, and cloud portability while maintaining seamless service for hundreds of millions of projects. The upgrade was motivated by growing concerns about AI agent containment and isolation, as autonomous agents require stronger security boundaries than traditional systems provide. The new engine, which began rolling out in February 2025, supports persistent workspaces, higher concurrency, and works across multiple cloud providers including AWS, Google Cloud, and Azure.