Claude Code Now Runs on Bun Written in Rust for Better Performance
Claude Code uses Bun written in Rust now
I investigated whether Claude Code is truly using the new Rust version of Bun. By inspecting the binary, I found evidence of a preview Bun v1.4.0 and numerous Rust source files embedded within. This confirms that the Rust port is running in production on millions of devices, delivering a 10% startup speed boost on Linux while remaining largely unnoticed by users.
"Boring is good."
HN discussion
- One user reports severe stability issues with Claude Code on Windows PowerShell, describing it as the least reliable program on their machine with unaddressed input bugs.
- Critics argue that rewriting a terminal UI in JavaScript via React and Bun is an engineering misstep, likening it to 'eating yogurt with a hammer' when a native rewrite would be cheaper and more robust.
- Defenders suggest the decision to use Bun was strategic to preserve the value of Anthropic's acquisition and to align with coding models that may prefer JavaScript runtimes for future tooling.
- Practitioners note that while Bun offers superior performance as a JavaScript runtime, its stability remains poor compared to Node, with reports of segfaults occurring 20x more frequently.
- Users observe that the high CPU utilization and heat generated by Claude Code stem from single-threaded execution rather than inherent slowness of the JavaScript language or V8 engine.