The document discusses new features in Servlet 3.1, including non-blocking I/O, protocol upgrades, security enhancements, and other features. Non-blocking I/O adds new ReadListener and WriteListener interfaces and methods to ServletInputStream and ServletOutputStream to support asynchronous and upgraded protocols. Protocol upgrades allow servlets to transition to other protocols like WebSocket using a new HttpUpgradeHandler interface. Security is enhanced with features like changing the session ID and clarifying the scope of run-as.