bun

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`bun init` automatically creates a Claude.md file by default
2 months ago
- Bun can initialize a project with `bun init` and accept defaults using `-y` flag.
- It creates package.json, tsconfig.json/jsconfig.json, entry point (default index.ts), README.md, and optionally CLAUDE.md or Cursor rules.
- The command runs `bun install` at the end to install `@types/bun`.
- Options include `--help` (-h), `--yes` (-y) to accept prompts, and `--minify` (-m) for type definitions only.
- Project templates are available via `--react` with presets like `tailwind` or `shadcn`.
- Output files vary by template and include project configuration and scaffolding.
Claude Code uses Bun written in Rust now
2 months ago
- Jarred Sumner claimed Claude Code v2.1.181+ uses the Rust port of Bun, resulting in 10% faster startup on Linux.
- Evidence from strings command shows Bun v1.4.0 (a preview version) and 563 .rs source files embedded in Claude Code.
- The Rust version of Bun is now available as a canary release via `bun upgrade --canary`.
- A simple script can confirm the embedded Bun version by running `BUN_OPTIONS="--preload=/tmp/bun-version.ts" claude --version`.
- The commit updating Bun's version to 1.4.0 was made on May 17th, but hasn't been tagged in a stable release.
Buz – A fork of Bun using modern Zig, with sub-1s incremental builds
2 months ago
- Buz is a work-in-progress fork of Bun, based on the last commit before its Rust rewrite, and is not ready for production.
- The project has been ported to build with the current upstream Zig, with a complete build graph in build.zig, enabling sub-1s incremental builds.
- The goal is to be a drop-in replacement for Bun with a cleaner codebase, having imported all new tests from Rust Bun and removed over 11,000 lines of dead code.
- The codebase has been rewritten and modernized, relying more on Zig's stdlib, fixing countless bugs in the process.
- The project uses a slightly patched Zig master submodule but can be built with upstream Zig at commit 2b1c663.
- Human-coded contributions are not accepted until the project is deemed sane enough, with LLMs used extensively for code generation to reduce technical debt.
- The author aims to create a maintainable drop-in replacement for Rust Bun 1.4.0 within weeks or months, focusing on idiomatic Zig and reducing slop code.
Claude Code uses Bun written in Rust now
2 months ago
- Jarred Sumner announced Claude Code v2.1.181+ uses Rust port of Bun, speeding up Linux startup by 10% with little user notice.
- Evidence found in Claude Code installation shows Bun v1.4.0 (macOS arm64), a version not yet released on GitHub as of the text's date.
- Rust version of Bun is available as a canary release, and 563 Rust source files in Claude indicate it's running in production.
My Thoughts on the Bun Rust Rewrite
2 months ago
- Jarred initially had 'beginner energy' which was healthy for learning but led to mediocre engineering outcomes.
- After Bun took venture capital and became a startup, Jarred's management style caused issues: poor communication, unrealistic expectations, and low empathy.
- The Zig team found Bun's codebase problematic with hacks, abuse of assertions, and reckless feature development, leading to social distance.
- The relationship between Zig and Bun deteriorated, culminating in relief when Bun was acquired by Anthropic and stopped donations.
- The Rust rewrite announcement was welcomed by the Zig team to distance themselves from Bun's engineering practices.
- The blog post about the rewrite is criticized for misrepresenting bug elimination, test suite effectiveness, and performance improvements.
- Zig's compiler performance is highlighted as efficient compared to Bun's unmentioned compilation speed post-rewrite.
- Despite criticisms, there is gratitude for Bun's donations to Zig and no personal ill will towards Jarred, but happiness that business interests are no longer intertwined.
Rewriting Bun in Rust
2 months ago
- Bun has been rewritten from Zig to Rust using AI-powered coding agents, significantly reducing memory-related bugs.
- The rewrite was enabled by a comprehensive TypeScript test suite that served as a conformance benchmark for automated porting.
- Key engineering techniques included dynamic workflows, trial runs, adversarial review, and process-based fixes rather than manual code editing.
- Jarred Sumner praised Zig for Bun's initial development but chose Rust for its memory safety features like RAII and compiler checks for use-after-free errors.
- The rewrite took about 11 days of intensive AI-assisted work, with an estimated cost of $165,000 in API tokens, funded by Anthropic.
- The new Rust version has been live in Claude Code for nearly a month, improving startup speed by 10% on Linux with minimal user impact.
- The project demonstrates how advanced language models can enable ambitious, large-scale software rewrites previously considered infeasible.

`bun init` automatically creates a Claude.md file by default

Claude Code uses Bun written in Rust now

Buz – A fork of Bun using modern Zig, with sub-1s incremental builds

Claude Code uses Bun written in Rust now

My Thoughts on the Bun Rust Rewrite

Rewriting Bun in Rust