What Does It Mean When AI Coding Assistants Start Optimizing for Millisecond-Level Startup Times?

Let's start with the conclusion: Claude Code integrating the Rust-refactored Bun has improved Linux boot speed by 10%. This is absolutely not just a simple runtime swap; it's a signal that AI coding tools are evolving from "calling models" to "embedding into execution environments." As the dependency chain shifts from Node.js to Bun, combined with the memory safety and performance gains from the Rust refactor, what we're seeing is an engineering surgery targeting interaction latency—under the scalpel lie accumulated tens of milliseconds, which could reshape developers' perception of the "instant feel" of AI assistants.