Claude Code Integrates Rust-Based Bun, Achieving 10% Faster Linux Startup
Claude Code version v2.1.181 now incorporates Bun, rewritten in Rust, leading to a 10% faster startup time on Linux platforms.
Developer Simon Willison reported on July 19 that Claude Code version v2.1.181, released on June 17, has integrated Bun, a JavaScript and TypeScript runtime environment that has been refactored in the Rust programming language. This integration has resulted in a 10% increase in startup speed on the Linux operating system.
Bun serves as the runtime environment for executing JavaScript and TypeScript programs. While Claude Code is distributed as a standalone executable file, its underlying program utilizes Bun as its operational environment. This shift to Rust marks a significant technical evolution for Bun.
Earlier, developer Jarred Sumner announced the complete rewrite of Bun from Zig to Rust, a process reportedly completed in 11 days with the assistance of the Claude Fable 5 model, at a cost of $165,000.
Upon examining Claude Code's executable file, Willison observed references to "Bun v1.4.0" and numerous strings resembling Rust source file names, indicated by the ".rs" extension. This technical evidence confirms the adoption of the Rust-based Bun runtime.