@jarredsumner

building @bunjavascript at @anthropicai. formerly: @stripe (twice) @thielfellowship. high school dropout. npm i -g bun

 San Francisco, CA
bun.com
Joined May 2014
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People frequently ask: > How is Bun sustainable? If I bet my company’s tech stack on Bun, will Bun still be around in a few years? We didn’t have a great answer to this question, until today
Bun
@bunjavascript2 Dec 2025
Bun is joining Anthropic! bun.com/blog/bun-joins-anthr…

Bun is joining Anthropic

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.

bun.com
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Jarred Sumner retweeted
Bun
@bunjavascript2h
Bun v1.4.4 - Fixes 271 issues, addressing 544 👍 - `bun fmt` is a fast Prettier-compatible code formatter - `bun check` gets 1.4x - 7.8x faster - New in Bun.SQL & WebSocket - Security fixes, including for Brotli, TLS certs, HTTP/3, and more bun.com/blog/bun-v1.4.4

Bun v1.4.4

Fixes 271 issues, addressing 544 👍. bun fmt, a Prettier-compatible formatter built into Bun that is 3x to 6x faster than oxfmt, bun check is 1.4x to 7.8x faster on large projects, bun install...

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a lot of my job now is telling claude “you need to think bigger”
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4th attempt at Bun AOT. Code quality & design is better. Perf is nearly there. Most importantly though It’s just TypeScript. Disregard everything I said last week about `as` casts changing runtime behavior and function arguments throwing. None of that is necessary.
Jarred Sumner
@jarredsumnerOct 19
this was my 3rd attempt at Bun AOT. the first two were before `bun check`, and performed worse than the JIT. it used bytecode instead of typescript types. binaries were sometimes 1 GB lol trying attempt 4 now. doesn’t work yet
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The remaining runtime behavior change, which the 3rd attempt also did, is a JavaScript behavior change that is small and also security hardening Object.prototype is “locked”, and a handful of other JavaScript builtins can’t be reassigned / writable. This impacts some polyfills.
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Jarred Sumner retweeted
alistair
@alistaiirOct 21
A year ago I would not have believed you if you told me Bun would get a formatter, a linter, and a type checker, and be (re)written in Rust, all in like 4 months
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i genuinely think good AOT JS/TS with full ecosystem compatibility would be the most exciting thing to happen to JavaScript since Node
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the knock on server-side JS has always been that you only use it because you already know it. rEaL enGiNeeRs use Go or RuSt LLMs know every language so that doesn't matter anymore, but the substance behind that knock is still true - JS uses more memory and CPU
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however, LLMs are also really good at writing compilers. so instead of you rewriting your app in another language, what if we just rewrite the compiler to make JS/TS perform competitively with Go and Rust then rewriting your app might not be worth it, even if it’s easy
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this was my 3rd attempt at Bun AOT. the first two were before `bun check`, and performed worse than the JIT. it used bytecode instead of typescript types. binaries were sometimes 1 GB lol trying attempt 4 now. doesn’t work yet
Jarred Sumner
@jarredsumnerOct 17
big draft pr github.com/oven-sh/bun/pull/…

Compile TypeScript to machine code ahead of time: `bun build --compile --aot` by Jarred-Sumner ·...

bun build --compile --aot compiles TypeScript and JavaScript to machine code when you build. The executable has no JIT and no bytecode, and it never asks the OS for executable memory. The TypeScrip...

github.com
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Why are there like six parsing passes? Why does the trimmer think Bun.Archive is in use when you have a property named “Archive” somewhere? The results are exciting, but these questions sound like a bug farm.
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I want this to be good. So another implementation, with a more refined design seems worth it. But the same underlying idea - TypeScript types -> IR as the starting point. sound types when proven, predictions, or unknown
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In the next version of Bun bun check gets 1.7x - 7x faster
Benchmark chart for bun check, Bun's built-in TypeScript type checker. It compares Bun canary, Bun 1.4.3 and tsc 7.0.2 on four projects, showing time and peak memory for a full type check. mui docs: canary 1.31s, 1.5 GiB. Bun 1.4.3 9.31s, 9.6 GiB, 7.1x slower. tsc 18.04s, 8.3 GiB, 13.8x slower. t3code server: canary 1.47s, 1.5 GiB. Bun 1.4.3 4.53s, 1.6 GiB, 3.1x slower. tsc 22.02s, 7.1 GiB, 15.0x slower. supabase studio: canary 0.63s, 1.6 GiB. Bun 1.4.3 1.67s, 1.9 GiB, 2.7x slower. tsc 8.98s, 4.5 GiB, 14.3x slower. mikro-orm: canary 1.24s, 1.6 GiB. Bun 1.4.3 2.15s, 2.0 GiB, 1.7x slower. tsc 13.41s, 6.8 GiB, 10.8x slower. Benchmarked on a 64-core machine (EPYC 9R14, Linux x64). No cache, default settings.

ALT Benchmark chart for bun check, Bun's built-in TypeScript type checker. It compares Bun canary, Bun 1.4.3 and tsc 7.0.2 on four projects, showing time and peak memory for a full type check. mui docs: canary 1.31s, 1.5 GiB. Bun 1.4.3 9.31s, 9.6 GiB, 7.1x slower. tsc 18.04s, 8.3 GiB, 13.8x slower. t3code server: canary 1.47s, 1.5 GiB. Bun 1.4.3 4.53s, 1.6 GiB, 3.1x slower. tsc 22.02s, 7.1 GiB, 15.0x slower. supabase studio: canary 0.63s, 1.6 GiB. Bun 1.4.3 1.67s, 1.9 GiB, 2.7x slower. tsc 8.98s, 4.5 GiB, 14.3x slower. mikro-orm: canary 1.24s, 1.6 GiB. Bun 1.4.3 2.15s, 2.0 GiB, 1.7x slower. tsc 13.41s, 6.8 GiB, 10.8x slower. Benchmarked on a 64-core machine (EPYC 9R14, Linux x64). No cache, default settings.

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big draft pr github.com/oven-sh/bun/pull/…

Compile TypeScript to machine code ahead of time: `bun build --compile --aot` by Jarred-Sumner ·...

bun build --compile --aot compiles TypeScript and JavaScript to machine code when you build. The executable has no JIT and no bytecode, and it never asks the OS for executable memory. The TypeScrip...

github.com
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going to rewrite about half of it. not good enough yet.
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We’re likely going to do this because schema validation libraries are basically the worst case scenario for AOT performance without compiler integration github.com/oven-sh/bun/issue…

Integration of a Validation Library into Bun · Issue #6797 · oven-sh/bun

What is the problem this feature would solve? Integrate a robust validation library into Bun to streamline data validation for developers, enhancing the utility and efficiency of using Bun. Additio...

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Here's a little how Bun AOT currently works (and may still change a lot): 1. bun build --compile --aot <script> 2. `bun check` type-checks but allows untyped code 3. Typed IR 4. Optimization passes 5. JavaScriptCore's B3 compiler runs 6. ARM64/x64 machine code (continued)
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JSON.stringify's fast path for typed objects makes JSON.stringify 2.2x faster in this benchmark. Untyped objects or typed objects with extra properties fallback to the generic JSON.stringify
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RegExp literals get compiled ahead of time
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