Bun has joined Anthropic — and Anthropic is betting on Bun
NEWBun v1.4.2 released

Bun is a fast JavaScript runtime & toolkit. All in one.

Runtime, package manager, test runner and bundler in a single binary. Use bun install or bun test in an existing Node.js project, or run the whole thing on Bun.

Install Bun v1.4.2

curl -fsSL https://bun.sh/install | bash
View install script ↗
Then follow the quickstart

Installing a Next.js app

warm cache · seconds (lower is better)

bun
v1.4
0.21s
yarn
v1.22.22
1.76s
pnpm
v11.21.0
1.92s
npm
v12.0.2
4.45s
T3-stack app, 25 direct dependencies, ~220 packages in the lockfile · warm cache · lockfile present · node_modules removed · Linux x64, EPYC 9R14 · every package manager at defaults · medians of 3reproduce

Used by

Four tools, designed together.
Adopt one, or all of them.

bun install and bun test drop into existing Node.js projects. No runtime switch required.

Runtime

replaces Node.js

Runs JavaScript & TypeScript on JavaScriptCore. Node.js APIs, node_modules and your framework work as-is.

$ bun run index.tsx

Package manager

replaces npm · yarn · pnpm

npm-compatible, up to 30× faster. Workspaces, catalogs, overrides, patches and a lockfile you can read.

$ bun install

Test runner

replaces Jest · Vitest

Jest-compatible expect(), mocks, snapshots, DOM and coverage — starting in milliseconds.

$ bun test

Bundler

replaces esbuild · Vite · webpack

TS, JSX, CSS & HTML for browsers and servers. Dev server with HMR. Single-file executables.

$ bun build ./app.tsx

A minute with Bun

One binary for the whole workflow.

Install, develop, run, test and ship with the same tool. Every step below is a real command with real output.

v1.4.2Latest release · September 2026

Elysia regression fixed. Upgraded JavaScriptCore. CMYK JPEGs in Bun.Image.

Bun 1.4.2 fixes 7 issues, including two v1.4.1 regressions: a bun build rename bug impacting Elysia apps and an AsyncLocalStorage memory leak. It also fixes worker_threads 'online' ordering, GC and JIT crashes, CMYK JPEG decoding in Bun.Image and a bun install lockfile panic, and upgrades JavaScriptCore.

Read the release notes$ bun upgrade

In production

Bun in production

Claude Code ships to millions of developers as a Bun executable. Midjourney pushes every image notification through Bun's WebSocket server. Railway runs its serverless functions on it. Hear it from them:

Claude Code

Claude Code ships to every developer as a Bun single-file executable.

Claude Code is a single file with Bun inside it. Users download it and run it. There is no install step and no startup lag.

Single-file executables

Midjourney

Every image notification Midjourney sends goes through Bun's WebSocket server.

Pub/sub, backpressure and per-message compression are built into Bun.serve() — no ws, no socket.io, no sidecar.

Bun's WebSocket server

Railway

Railway built its serverless Functions product on Bun.

A Railway Function is a TypeScript file. Bun runs it as-is, so a deploy skips the build and a cold start takes milliseconds.

Deploy on Railway

Frameworks

Bun runs Next.js, Remix, Nuxt, Astro, SvelteKit, Hono, Elysia & friends.

Node.js compatibility means your framework already works. Swap npm run dev for bun --bun run dev and keep shipping — with Bun's SQL, S3 and shell APIs available right inside your route handlers.

app/blog/[slug]/page.tsx
import { s3, $, sql } from "bun";
 
export default async function BlogPage({ params }) {
  const [post] = await sql`SELECT * FROM posts WHERE slug = ${params.slug}`;
  const img = s3.file(post.imageKey).presign();
  const words = await $`wc -w < ${post.file}`.text();