Every agent framework ships its own UI. Every team builds their own chat interface, tightly coupled to whatever backend they chose. AG-UI is an open protocol that breaks that lock-in, a standard event stream that lets any agent backend plug into any compatible frontend. Swap your backend without touching your UI. This talk walks through what AG-UI is, why it matters for anyone building agentic applications, and what I learned building and merging the Claude Agent SDK integration into the protocol, including the tricky bits around session persistence, stateful tool handling, and human in the loop.