A2UI v0.9: What's New in Google's Generative UI Spec

A2UI v0.9 is Google's open protocol for Generative UI, enabling agents to send declarative component descriptions that clients render using their own native widgets. Key changes from v0.8 include a prompt-generate-validate loop replacing structured output constraints, flat standard JSON replacing wrapper objects, bidirectional messaging so agents know UI state when users act, modular schema split into four files, catalog negotiation handshake, and a new Agent SDK. The post also covers how to wire any agent in five steps using the Python SDK, and how A2UI integrates with AG-UI protocol and CopilotKit for streaming UI to frontends without agents writing frontend code.