The Billion-Dollar Runtime That Finally Got My Attention

I'd see it mentioned on Twitter, read the occasional "wow, Bun is so fast!" post, and think "yeah, I should check that out sometime." Then I'd go back to writing Node.js code, dealing with npm install times, and generally being too busy to investigate yet another JavaScript runtime.

We've all been there. There's always something shinier, faster, or newer in the JavaScript ecosystem. Most of the time, it's easier to stick with what works - even if what works is a bit slower than it needs to be.

But then Anthropic made its first acquisition. They didn't buy another AI model or a data company. They bought Bun. And they dropped this number: Claude Code had reached $1 billion in run-rate revenue in just six months.

That made me stop scrolling. When a company growing that fast decides its JavaScript runtime is essential enough to acquire, maybe it's time to bump Bun up from "interesting curiosity" to "actually worth my time."

What I'd Been Missing (Apparently)

So I finally did what I should have done months ago: I actually read about what Bun does differently. And okay, I get it now.

If you've been writing JavaScript for any length of time, you know the tooling situation. You need Node.js for the runtime, npm or yarn for packages, Webpack or Rollup for bundling, Jest for testing, and probably ts-node if you want TypeScript support. Each tool has its own configuration files, quirks, and ways of slowing you down.

Bun just... doesn't do that. It's an all-in-one toolkit: runtime, package manager, bundler, and test runner in a single binary. No juggling multiple tools. No configuration hell.

But here's the part that made me sit up: instead of building on V8 like Node.js (and Deno, and pretty much everything else), Bun uses JavaScriptCore - the engine that powers Safari. At first, that seems weird. Why not use the engine everyone else uses?

Then you realise what JavaScriptCore was optimised for: fast startup times and low memory usage. V8 is brilliant for long-running processes, but JSC was designed for scripts that start quickly and run briefly, which is precisely what you need for developer tools.

When you run bun install, and it finishes in a second instead of thirty, that's not magic. It's choosing the right tool for the job.

The Zig Thing (Which I Had to Look Up)

Here's where it gets interesting. Bun isn't written in JavaScript, TypeScript, or even the usual suspects like C++ or Rust. It's written in Zig.

I had to Google what Zig even was. Turns out it's a systems programming language that's still at version 0.15 - not even 1.0 yet. Building your entire runtime on a language that doesn't promise stability seems... bold? Reckless? Both?

But Jarred Sumner (Bun's creator) had his reasons, and they actually make sense. Zig sits in the same performance tier as C and C++ - compiling directly to machine code with no garbage collection overhead. But unlike C++, which has accumulated decades of complexity (templates, multiple inheritance, exceptions, the preprocessor doing mysterious things), Zig is deliberately simple. What you see is what you get.

More importantly for Bun's case: Zig can directly call C and C++ code without needing bindings or FFI layers. Since Bun requires integration with JavaScriptCore (written in C++), Zig made that straightforward. Rust or Go would have added friction.

And cross-compilation? Zig just does it out of the box - no fighting with platform-specific toolchains. For a small team trying to ship on macOS, Linux, and Windows, that matters.

Why the Acquisition Changed My Mind

Here's the thing about JavaScript tooling: there's always something new. Deno was going to replace Node. Then Deno 2.0 was going to replace Node. Before that, it was something else. After Bun, it'll be something else again.

When you're busy shipping actual code, you learn to tune out most of the noise. "Fast JavaScript runtime" sounds great until you remember you have deadlines, and migrating infrastructure is never as simple as the benchmarks suggest. You develop a healthy scepticism about tools that promise to change everything.

But the Anthropic acquisition is different. They weren't just kicking the tyres or trying to be cool. They'd been using Bun in production for months as essential infrastructure for Claude Code. The native installer? Built on Bun. The ability to handle enterprise clients like Netflix and Spotify? Running on Bun. That $1 billion in revenue growth? Bun was the load-bearing infrastructure for it all.

When you're growing that fast, you don't have time for nice-to-have tools. You acquire the things that will break your product if they go away. You develop the infrastructure you've already bet on and can't afford to lose.

This is what got my attention. Not the benchmarks. Not the "we're so much faster than Node!" marketing. The fact that a company with everything to lose decided that Bun was critical enough to buy.

That's the kind of signal that cuts through all the usual JavaScript ecosystem noise.

What This Actually Means for People Like Me

For developers who've been curious about Bun but never quite prioritised it, the acquisition changes the risk calculation.

The project stays open-source and MIT-licensed. Same team, same public development on GitHub. But now it has the backing of a company generating billions in revenue - and a company that will break if Bun breaks.

Claude Code ships as a Bun executable to millions of users. If Bun has a critical bug, so does Claude Code. Anthropic now has a straightforward incentive to keep Bun not just functional, but excellent.

That's different from a VC-backed startup promising they'll figure out monetisation later. Jarred Sumner (Bun's creator) wrote candidly about this in the acquisition announcement: Bun had raised $26 million but was making zero revenue. Joining Anthropic meant they could skip the "try to figure out how to charge for this" phase and just focus on creating great tools.

For someone deciding whether to invest time learning a new runtime, "backed by a company that depends on it staying excellent" is a much better answer than "they raised $26 million."

The Bigger Picture (That I'm Choosing to Care About Now)

Something interesting is happening here that goes beyond just "a new tool is faster."

AI coding tools already default to JavaScript and TypeScript unless you tell them otherwise. With Anthropic acquiring Bun, that pattern is likely to strengthen. When the company building the most successful AI coding tool also owns the fastest JavaScript runtime, they're making a clear bet on where development is headed.

This might bother people who think JavaScript should be retired (and they're not wrong about its flaws). But ubiquity matters. Every developer knows JavaScript. Every platform runs it. Sometimes the tool that's everywhere beats the perfect tool.

The acquisition also signals infrastructure priorities. The companies winning in AI aren't just building better models - they're acquiring the tooling that makes development with those models fast and reliable. Developer experience isn't a nice-to-have anymore. It's the constraint that determines whether you scale or hit a wall.

For those of us writing code every day, this translates pretty simply: the tools we use matter more than we might think. A faster package manager isn't just a luxury. Quicker test execution isn't just convenience. When you multiply small time savings across hundreds of developers or thousands of operations, it becomes the difference between shipping and struggling.

Why I'm Actually Going to Try It Now

The best part about Bun being a drop-in replacement? There's almost no commitment required. I can literally try it on my next project without rewriting anything.

Here's what that looks like:

# Instead of:

node index.js

# Just use:

bun index.js

Same code. Same package.json. Same dependencies. Just swap the runtime.

Package management works the same way. npm install becomes bun install. npm run dev becomes bun run dev. TypeScript and JSX files run without needing to configure anything - no ts-node, no babel, it just works.

This is the incremental adoption that actually happens in the real world. I'm not going to rewrite my entire stack on a weekend. But I can absolutely try bun install on Monday and see if the speed difference is as noticeable as people claim. If it is, I can try bun run for my dev scripts. If something breaks - and yes, some packages will have issues - Node.js is still installed, and I can switch back.

The compatibility isn't perfect. Some packages, particularly WebSocket libraries or specific native modules, might hit edge cases. Debugging isn't quite as mature. Monorepos can surface weird behaviour. But for straightforward applications? Most things just work. Express, Next.js, and most npm packages run without modification.

And now that Anthropic owns it, those compatibility gaps are going to close fast. When your billion-dollar product depends on it, fixing bugs becomes extremely high priority.

Why It's Finally Moving Up My List

I've kept putting off trying Bun because I was busy. Busy writing Node.js code. Busy shipping features. Busy dealing with the usual thousand small fires that come with software development.

But here's what changed: the risk-reward calculation is different now. Before, Bun was an interesting experiment from a small startup. Fast? Sure, probably. Worth the time to investigate? When I get around to it. Worth betting a project on? Not really.

Now it's the infrastructure for a billion-dollar product. It's backed by a company that absolutely cannot let it fail. It's proven itself at scale with enterprise clients that have zero tolerance for tools that break.

More importantly, trying it costs me almost nothing. Install it, run bun install on my next project, see what happens. Suppose it's noticeably faster, great. If it's not, or if I run into compatibility issues, Node.js is right there, and I'm out in 15 minutes.

That's a bet I'm willing to make. Not because Bun is perfect - it's not. Not because the JavaScript ecosystem needs another runtime - it probably doesn't. But because sometimes the tools you use actually matter, and a company growing that fast just told us this one matters to them.

So yeah. Bun just moved from "interesting someday" to "actually going to try this week." If you've been in the same boat - curious but busy, interested but sceptical - it's time to bump it up your list too.

The worst case? You spend twenty minutes confirming that Node.js is fine and you don't need to change anything. The best case? Your builds get faster, and you wonder why you waited so long.

Either way, at least you'll know.

Related Articles