AG-UI (Agent User Interaction Protocol) is an open, event-based protocol that standardizes how AI agents communicate with user-facing applications. Created by CopilotKit and adopted by Microsoft, Google, AWS, LangChain, and CrewAI, it fills the gap between MCP (agent↔tools) and A2A (agent↔agent) by defining the agent↔UI layer. It's MIT licensed with 14.4k GitHub stars and 50+ framework integrations.
The Model Context Protocol specification release candidate (locked May 21, stable July 28, 2026) makes the protocol fully stateless — no handshakes, no session IDs, no sticky routing. Alongside that headline change, it graduates the extensions framework to first-class status, introduces MCP Apps for server-rendered UI, formalizes the Tasks extension for long-running work, adds production-grade observability headers, upgrades to full JSON Schema 2020-12, and hardens OAuth 2.0 authorization through multiple SEPs. Three features — Roots, Sampling, and Logging — are deprecated under a new lifecycle policy with a one-year sunset window.