Jarred Sumner
@jarredsumner

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

 San Francisco, CA
bun.com
Joined May 2014
3,990 Photos and videos
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
@bunjavascript
2 Dec 2025
Bun is joining Anthropic! bun.com/blog/bun-joins-anthr…
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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
@jarredsumner
Oct 17
big draft pr github.com/oven-sh/bun/pull/…
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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...

github.com
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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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A year ago, I would've said a linter, a formatter and a type checker were too ambitious for Bun. But for ahead of time compiled TypeScript to have a shot at being something people use, it will need integrated tooling.
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A Prettier-compatible formatter, builtin to Bun.
Bun
@bunjavascript
Oct 13
In the next version of Bun `bun fmt` is a 320x faster Prettier alternative Passes 99% of Prettier's test suite & supports 20 languages
Poster for bun fmt, a Prettier-compatible formatter built into Bun. Headline: 320x faster than Prettier. Bar chart of wall-clock time to run --check on microsoft/vscode (10,148 files, 8 cores): bun fmt 0.43 s, oxfmt 0.72 0.85 s (2x slower), Biome 2.5 3.6 s (8.3x slower), Prettier 3.9.9 139 s (320x slower). Formats 20 languages: JavaScript, TypeScript, JSX, Flow, HTML, Vue, Angular, Handlebars, MJML, CSS, SCSS, Less, JSON, JSONC, JSON5, YAML, TOML, GraphQL, Markdown and MDX. 99% of Prettier's tests pass (9,728 of 9,821). 5x less memory than Prettier (183 MB vs 972 MB).

ALT Poster for bun fmt, a Prettier-compatible formatter built into Bun. Headline: 320x faster than Prettier. Bar chart of wall-clock time to run --check on microsoft/vscode (10,148 files, 8 cores): bun fmt 0.43 s, oxfmt 0.72 0.85 s (2x slower), Biome 2.5 3.6 s (8.3x slower), Prettier 3.9.9 139 s (320x slower). Formats 20 languages: JavaScript, TypeScript, JSX, Flow, HTML, Vue, Angular, Handlebars, MJML, CSS, SCSS, Less, JSON, JSONC, JSON5, YAML, TOML, GraphQL, Markdown and MDX. 99% of Prettier's tests pass (9,728 of 9,821). 5x less memory than Prettier (183 MB vs 972 MB).

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A TypeScript-compatible type checker, builtin to Bun.
Bun
@bunjavascript
Oct 6
In the next version of Bun `bun check` is a TypeScript type checker builtin to Bun (written in Rust)
Announcement graphic for bun check, a TypeScript type checker built into Bun, with the Bun logo. A bar chart compares type checking VS Code (10,947 files). bun check: 1.75s, 2.77 GiB. tsc 7 with --checkers 16: 5.88s, 9.23 GiB. tsc 7 (typescript-go) with default settings: 12.58s, 7.73 GiB. bun check is 3x to 7x faster with 2.8x to 3.3x less memory. Linux x64, 64 threads, mean of 20 runs. Passes 100% of TypeScript's conformance tests. "Thank you, TypeScript team. bun check is a port of typescript-go."

ALT Announcement graphic for bun check, a TypeScript type checker built into Bun, with the Bun logo. A bar chart compares type checking VS Code (10,947 files). bun check: 1.75s, 2.77 GiB. tsc 7 with --checkers 16: 5.88s, 9.23 GiB. tsc 7 (typescript-go) with default settings: 12.58s, 7.73 GiB. bun check is 3x to 7x faster with 2.8x to 3.3x less memory. Linux x64, 64 threads, mean of 20 runs. Passes 100% of TypeScript's conformance tests. "Thank you, TypeScript team. bun check is a port of typescript-go."

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