Claude Code теперь работает на Bun, переписанном на Rust: старт на 10% быстрее

Claude Code, starting with version 2.1.181, released on June 17, 2026, runs on the Bun runtime, rewritten from the Zig language to Rust. The switch was reported by Bun's creator Jarred Sumner, and on July 19, 2026, developer Simon Willison independently confirmed it by examining the Claude Code binary: startup on Linux became about 10% faster.

How Rust was discovered inside Claude Code

Simon Willison confirmed the switch by running the `strings` command on the Claude Code binary, filtering for the string "Bun v1". The output was `Bun v1.4.0 (macOS arm64)`. A second command, searching for paths like `src/*.rs`, returned a list of 563 file names with the `.rs` extension — from `src/runtime/bake/dev_server/mod.rs` to `src/bundler/bundle_v2.rs`. This is direct evidence that it is Rust runtime code that is compiled into the binary.

• Claude Code v2.1.181 — released June 17, 2026, the first version on the Rust port of Bun
• The bundled runtime is Bun v1.4.0; the stable Bun releases so far top out at v1.3.14 (May 12, 2026)
• The `strings` command found 563 file names with the `.rs` extension
• The startup speed gain on Linux is about 10%
• The Rust version is already publicly available as a canary build (`bun upgrade --canary`)

Why Claude Code ships Bun 1.4.0, which doesn't exist yet

Claude Code contains Bun v1.4.0 — a version that doesn't yet exist in stable Bun releases. The latest tag on GitHub is v1.3.14 from May 12, 2026, while the number 1.4.0 landed in `package.json` back in a commit from May 17, 2026, and hasn't changed since. In effect, Anthropic is shipping a pre-release build of the runtime inside a production tool used by millions of developers.

You can check the bundled version without `strings`, too. Developer Ajan Raj proposed a trick: load a script via the `BUN_OPTIONS` variable and call `claude --version` — the command prints `1.4.0`, the same runtime version.

"Boring is good" — what Bun's creator says

The switch went so smoothly that almost no one noticed anything. That's exactly the point Bun's creator is making: the main result of the Rust rewrite isn't flashy features, but stability and a slightly faster start.

"Claude Code v2.1.181 (released June 17) and later versions use the Rust port of Bun.

Startup on Linux got 10% faster, but almost no one noticed anything else. Boring is good," — Jarred Sumner, creator of Bun, in the blog post "Rewriting Bun in Rust."

Simon Willison agrees with the assessment: in his words, "Bun on Rust really is running in production on millions of different devices."

What this means

Anthropic is using Claude Code as a proving ground to field-test the new Rust version of Bun in real production before its stable release. For users this is unnoticeable — the CLI just starts up a bit faster; for the Bun ecosystem, this is a real-world stress test of the Rust port on a huge base of devices.

Frequently asked questions

What is Bun?

Bun is a fast JavaScript runtime and an alternative to Node.js, on which Claude Code runs. Bun was originally written in the Zig language, and now its core has been rewritten in Rust.

How do you check which version of

Bun is bundled in Claude Code?

You can run `strings ~/.local/bin/claude | grep -m1 'Bun v1'` — the output will show `Bun v1.4.0`. An alternative from Ajan Raj: run `claude --version` with the `BUN_OPTIONS` variable loading a script with `Bun.version` — the result is the same, `1.4.0`.

Has Claude Code gotten faster?

Yes, but not by much: according to Jarred Sumner, startup on Linux got about 10% faster. On other platforms the difference is barely noticeable to users.