Real-time blocking is runtime enforcement that stops or interrupts behavior as soon as it violates a security policy or crosses a boundary. Unlike a rule that is checked only before launch or after the fact, real-time blocking acts while a process, agent, or session is active.
In cyber security, this matters because many attacks succeed by chaining small actions quickly: opening a network connection, reading secrets, invoking tools, or moving into a forbidden system. Real-time blocking can cut off that sequence by denying the action, suspending the process, or terminating the session. Defenders use it in sandboxes, EDR and EPP products, web and API gateways, and agent controls for AI systems. In frontier AI environments, it helps prevent a model from calling unapproved tools, reaching live services, or escaping a test boundary. Its value is speed: when policy is enforced immediately, there is less chance for damage, exfiltration, or lateral movement.