Rivet Actors is a framework for building long-running, stateful agent processes. It runs actors with in-memory state that automatically persists to durable storage backends including Cloudflare Durable Objects and FoundationDB. Actors process messages from queues, integrate with LLM APIs for streaming responses, and broadcast events to connected clients in real-time. The system handles scheduling, workflows, and provides client SDKs for connecting to running agents from frontend or backend code.