React Under Fire: Rendering Performance for Streaming Agent UIs

I have three years of experience building interfaces for AI agents, currently at Slack, where I work on agentic AI surfaces. As a developer working in this area daily, I have seen a consistent pattern: React applications that perform well under normal user interaction degrade quickly when connected to a streaming agent, where a single response can produce dozens of state updates per second. In this session, I will cover the rendering and state management challenges specific to agentic UIs, drawing from production experience and from a public benchmark I built to measure rendering strategies under real agent event streams. The session will address three areas. First, state architecture: how partial and final text differ as state shapes, why conventional Redux patterns struggle with high-frequency token streams, and what alternatives exist. Second, implementation tradeoffs: when a streaming library is justified, when a custom buffering layer is the better choice, and how primitives like useSyncExternalStore fit in. I will demonstrate these comparisons through live coding, with performance measurements for each approach. Third, standards: what the AG-UI protocol currently specifies for agent-to-UI communication, and where it leaves decisions to the implementer.