June 3, 2026
Unsafe at Any Speed?
Bun Has Been Converted to Rust. Now What?
Fans call it bold, reckless, and very AI as Bun’s big rewrite sparks trust panic
TLDR: Bun replaced its old code with a huge AI-assisted Rust rewrite in days and passed almost all tests, but critics say the safety promise looks shaky because so much of the new code bypasses Rust’s protections. The comments quickly turned into a trust war: impressive feat or reckless AI stunt.
Bun, the fast JavaScript app tool that built a fan club by trying to outshine Node, just pulled off the kind of stunt that makes comment sections catch fire. Its creators merged a massive rewrite from Zig to Rust in just nine days, with AI coding agents doing almost all the work. The new version passed 99.8% of tests, and the app even got a little smaller and sometimes faster. On paper, that sounds like a win. In the comments? Absolute chaos.
The loudest reaction was basically: if the whole point was safety, why are there more than 10,000 “unsafe” sections in the new code? That became the central accusation — that this wasn’t a safety makeover so much as old risk wrapped in shinier packaging. One commenter flat-out called it “blatantly irresponsible” and said Bun had lost credibility. Others instantly turned this into a team sport, waving the flag for Deno, another JavaScript runtime already built in Rust, with the not-so-subtle message: there was already a safer option, and it wasn’t vibe-coded.
And then came the jokes. People couldn’t resist the meta-comedy: AI-written code, AI-written blog posts, AI-designed websites, all arguing about AI-written code. That irony hit hard, and commenters milked it for all it was worth. So yes, Bun shipped a huge rewrite. But the real release was a community meltdown over trust, hype, and whether passing tests is enough when a machine did the typing.
Key Points
- •Bun merged PR #30412 on May 14, replacing its Zig implementation with a Rust rewrite generated almost entirely by Claude Code agents over nine days.
- •The article says the new Rust codebase contains a little over one million lines of code and 6,755 commits.
- •The rewrite passed 99.8% of Bun’s existing test suite, which the article says demonstrates interface-level behavioral compatibility with the prior implementation.
- •Benchmarks were described as neutral to faster, and the binary reportedly shrank by a few megabytes from an approximately 93 MB Linux x64 baseline.
- •The article says Bun chose Rust for memory-safety reasons, but notes the rewrite includes more than 10,000 `unsafe` blocks across more than 700 files.