Microsoft introduced the open-source Agent Control Specification (ACS) to allow custom policy enforcement for AI agents at multiple execution points. The company also announced seven new in-house models at Build 2026, including MAI-Thinking-1, MAI-Transcribe-1.5, MAI-Voice-2, and MAI-Code-1-Flash. These developments coincide with Microsoft's renegotiated relationship with OpenAI and its expansion of proprietary model development.