How Flutter Developers Build a Lag-Free Typewriter Effect for AI Streaming Replies

A developer building an AI narrative app in Flutter tackled the challenge of creating a smooth typewriter animation for streaming LLM replies delivered via HTTP Server-Sent Events. To prevent excessive UI rebuilds from rapid chunk arrivals, a 50ms batching window was implemented to consolidate multiple chunks into a single state update. A StringBuffer accumulator was used instead of repeated string concatenation to avoid O(n²) performance degradation on longer replies. A 'skip animation' button went through three iterations before correctly revealing buffered text instantly while allowing the LLM to continue generating the full reply in the background. The article notes these core decisions around buffering, batching, and separating 'skip' from 'abort' apply equally to web and native streaming UI implementations beyond Flutter.