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Comment by alfanick | Hacker News Reader

I'm confused. Never heard of Bun until a few days ago here on HN. It's some nodejs wrapper thingy, written in Zig, and someone decided to use LLM to rewrite it in Rust. Is this a big deal? Who is even using this software? Why is this big?

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Bun isn't a node.js wrapper. It's an alternative to node.js that sits at roughly the same spot in the stack.

Node.js is a distribution of the V8 JavaScript engine (the thing that executes JavaScript in the Chrome browser), along with a bunch of standard library code written mostly in C++.

Bun is a distribution of the JavaScriptCore engine (the thing that executes JavaScript in the Safari browser), along with a bunch of standard library code written mostly in Zig (and now Rust). Bun's standard library is in many cases compatible with or inspired by the Node.js standard library, but with some changes for convenience and performance.

Answering “who is even using this software” is unfortunately missing in your answer. I am honestly curious. I’ve never seen it “in the wild” (in job descriptions, hearing from past colleagues, meetups etc). Only place I heard about it is HN and Twitter.

It's primarily used by people who tend to sit on the cutting edge e.g. startups and developers who follow the latest tools. It's not well worn enough to be adopted by slower enterprise environments. Bun is well known within web development but if you don't work in the space and don't keep up to date with modern tooling it's unlikely you would have awareness of it.

I'd say the most prominent user (and the reason why Anthropic acquired Bun) is Claude Code

To my limited knowledge, "serious" production systems most likely use Node.js instead of any alternatives, and I don't see any movement towards adopting Bun.

notably anthropic on a multibillion revenue product

I've never done any JavaScript development of any kind and had never heard of this either. I thought it was a package manager at first, but apparently it's an entire runtime.

My question is, if it's this trivial to rewrite Zig to Rust, and trivial in general to write Rust at all, why not just use Rust for your server side code in the first place? What's the value of continuing to use JavaScript and putting so much effort into the runtime?

Rust vs Zig "wars" etc.

Also at some point Bun was acquired by Anthropic. And some people feared that this will greatly influence Bun's development.

I don't think Rust vs. Zig has anything to do with why people are talking about this. It is a large piece of "real software" that underwent a full language transition in ~1 week using LLMs. That is a big deal regardless of the language and will be a case study regardless of how it turns out.

It’s a watershed moment. Basically one of the most controlled applications of an LLM into a robust codebase without regard for the implications of doing so.

Anthropic needed something like this and it must proceed flawlessly. My guess is that nothing will explicitly break. But that’s the difficulty of LLM generated code: nothing breaks. You sit with a codebase that swallows all errors and appears to be working. Silently failing makes debugging performance and behavior much harder.

>I don't think Rust vs. Zig has anything to do with why people are talking about this.

Maybe, but I've seen quite a few comments from people who felt sort of betrayed(?) by the decision. I feel like Bun was important for people as a project that advertises Zig and keeps it relevant even in it's current "pre 1.0" state.

which was obviously a reasonable reaction.

I think relatively few people are probably running Bun in production, but as a dependency management system and bundler for the JavaScript ecosystem, it's similar to `uv` from the Python ecosystem in how much faster it is compared to the most popular alternatives so it's fairly popular in that space.

PNPM is just as fast and much more reliable.

Agree with this. Been a long time pnpm user that also uses bun nowadays. Not much faster other than initial startup because pnpm uses Node.js

Although pnpm has also been trying to rewrite Rust before, they call it pacquet. It is currently being revisited

Bun is not a node.js wrapper, it is a node.js alternative. It had non-trivial adoption, tens of thousands of stars on github for whatever that's worth (before the AI spam took over stars). It was then purchased by Anthropic and now we're witnessing open source software that people used be sacrificed to the altar of LLM marketing hype.

Not mature enough for everyone to be using it yet, but it may dominate the space down the line. They compete with Deno.

>Is this a big deal? Who is even using this software? Why is this big?

Let's see. $10T in market cap, a significant chunk of everyone's assets and retirement funds, are currently dedicated to AI build out because of the potential for AI like Claude Code, which is recently doing $3b in revenue, and built completely on Bun.

If Bun is able to successfully vibe code a complete language shift in this short of time, it much more concretely validates the potential of vibe coding / AI for the entire industry.

Bun has a lot of buzz as 'the next big thing' in the JS ecosystem, and was recently purchased by Anthropic. So it's kind of in the zeitgeist.

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