Claude Code uses Bun written in Rust now
This technical note confirms that Claude Code has transitioned to using a Rust-based version of the Bun runtime. The author verifies this by inspecting binary strings and notes the performance improvements.
Why it matters
It highlights the industry trend of rewriting core infrastructure tools in memory-safe languages like Rust for better performance and reliability.
In Rewriting Bun in Rust Jarred Sumner made the following claim:
Claude Code v2.1.181 (released June 17th) and later use the Rust port of Bun. Startup got 10% faster on Linux but otherwise, barely anyone noticed. Boring is good.
I decided to have a poke at my own Claude Code installation to see if I could find evidence that it was using Bun written in Rust.
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