Bun is joining Anthropic

Bun is joining Anthropic | Bun Blog Bun is joining Anthropic

 Jarred Sumner · December 2, 2025 TLDR: Bun has been acquired by Anthropic. Anthropic is betting on Bun as the infrastructure powering Claude Code, Claude Agent SDK, and future AI coding products & tools.

 What doesn't change: 

 Bun stays open-source & MIT-licensed
 Bun continues to be extremely actively maintained
 The same team still works on Bun
 Bun is still built in public on GitHub
 Bun's roadmap will continue to focus on high performance JavaScript tooling, Node.js compatibility & replacing Node.js as the default server-side runtime for JavaScript
 Claude Code ships as a Bun executable to millions of users. If Bun breaks, Claude Code breaks. Anthropic has direct incentive to keep Bun excellent.

 What changes: 

 We will help make coding tools like Claude Code & Claude Agent SDK faster & smaller
 We get a closer first look at what's around the corner for AI coding tools, and make Bun better for it
 Bun will ship faster.
 How Bun started 

 Almost five years ago, I was building a Minecraft-y voxel game in the browser. The codebase got kind of large, and the iteration cycle time took 45 seconds to test if changes worked. Most of that time was spent waiting for the Next.js dev server to hot reload.

 This was frustrating, and I got really distracted trying to fix it.

 I started porting esbuild's JSX & TypeScript transpiler from Go to Zig. Three weeks later, I had a somewhat working JSX & TypeScript transpiler.

 Early benchmark from a new JavaScript bundler. It transpiles JSX files:
- 3x faster than esbuild
- 94x faster than swc
- 197x faster than babel pic.twitter.com/NBRt9ESu2d 

— Jarred Sumner (@jarredsumner) May 5, 2021 I spent much of that first year in a very cramped apartment in Oakland, just coding and tweeting about Bun.

 The runtime

 To get Next.js server side rendering to work, we needed a JavaScript runtime. And JavaScript runtimes need an engine to interpret & JIT compile the code.

 The start time difference between JavaScriptCore and V8 is interesting. JavaScriptCore seems to start around 4x faster.

It's possible this is due to the specifics of their respective CLIs though (rather than about JavaScript execution) pic.twitter.com/xd5tSbWf6p 

— Jarred Sumner (@jarredsumner) May 26, 2021 So after about a month of reading WebKit's source code trying to figure out how to embed JavaScriptCore with the same flexibility as what Safari does, I had the very initial version of Bun's JavaScript runtime.

 Bun v0.1.0 

 Bun v0.1.0 was released in July of 2022. A bundler, a transpiler, a runtime (designed to be a drop-in replacement for Node.js), test runner, and a package manager - all in one. We ended up reaching 20k GitHub stars in the first week.

 Introducing Bun - an incredibly fast all-in-one JavaScript runtime. https://t.co/Yt6tAcnBQs 

— Jarred Sumner (@jarredsumner) July 5, 2022 Those first two weeks after the release were one of the

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