Rabi Shanker Guha

An LLM is a non-deterministic token machine. A production UI has to be reliable, consistent, and fast every time. Generative UI lives in the gap between those two facts, and that gap is usually treated as a frontend problem when it is really an infrastructure problem. This talk is the engineering story of closing that gap. We started where most teams start: ask the model for JSON, validate it against a schema, and render the tree. It demos well, but breaks down in production. Deeply nested JSON streams slowly, malformed structures appear under load, half-finished objects cannot render, and the output drifts from the design system. I’ll show the reliability layer we built in OpenUI to fix this: a compact, line-oriented language that models emit more reliably than nested JSON; streaming with forward-reference hoisting so each line can render as it arrives; and validation that drops invalid fragments instead of crashing the interface. The result is near-zero malformed output, up to 3x faster rendering, and 67% fewer tokens than JSON in public, re-runnable benchmarks. I’ll also cover the tradeoffs, including where schema-validated JSON and native protocols still make sense.