At Build 2026, Microsoft introduced an open-source standard named Agent Control Specification (ACS), designed to provide developers with a unified and fine-grained approach to controlling AI agent behavior. ACS allows development, compliance, and security teams to jointly formulate policy rules and check these policies at multiple critical nodes, ensuring that agents operate within established constraints. These policies are defined in a single file, which can be migrated with the agent across different frameworks and environments without the need for repeated configuration, enhancing consistency in governance capabilities. Additionally, developers can integrate classifiers or connect to large language models within ACS to classify input and output content, predict outcomes, or determine response methods. Currently, ACS is released in SDK form, supporting multiple mainstream AI agent development frameworks and tools.