assistant-ui separates Agent Chat into headless React primitives, a conversation runtime, and backend adapters, so the UI does not have to bind directly to one model SDK's message state.
CopilotKit is more than a chat box. Its React components, AG-UI events, shared state, and interrupt flows connect an agent's execution to an existing product interface.
A2UI is an agent generative UI protocol open-sourced by Google on 2025-12-15: agents send declarative JSON describing UI intent, and clients render it natively using their own component catalog whitelist, layered on top of A2A. It launched at format v0.8 and iterated to v0.9 within three months.