Jarred Sumner

He recalled on the Syntax podcast in December 2022 that his first programming language was Ruby, starting with Ruby on RailsRuby on RailsRuby on Rails (often shortened to Rails) is an open-source, full-stack web application framework written in the Ruby programming language that builds database-backed web applications following the model–view–controller (MVC) pattern. Created by David Heinemeier Hansson and first publicly released in 2004, it is known for design principles such as “convention over configuration,” and companies including GitHub and Shopify use it in production.Open the full entry; after that he learned a little JavaScript, though he did not know it very well at that point, and later built a few iPhone apps in Objective-C.⁠[1]

In TechCrunchTechCrunchTechCrunch is an American technology news outlet founded in 2005 by Michael Arrington and Keith Teare and headquartered in San Francisco; it mainly covers technology companies, startups, and venture capital, and hosts events such as TechCrunch Disrupt. Its ownership passed successively through AOL, Verizon, and Yahoo, and in 2025 Regent announced its acquisition.Open the full entry’s July 2014 article he mentioned that his self-imposed discipline came early: “I pretended to be a student at MIT and went to lectures.”⁠[2]

His personal website states that he is a high school dropout.⁠[3]

Adweek wrote on October 16, 2012 that Jarred Sumner, 16, had launched two products that month: Lockitron, a device that lets people open doors with their mobile phones, and Selfstarter, an open-source alternative to Kickstarter. The article says that Kickstarter, which curates the projects it hosts, declined to host Lockitron’s pre-orders, so he and his colleagues wrote their own code, which they open-sourced on GitHub on a Thursday; by the following Monday it had been forked 150 times and 500 users were following the project.⁠[4]

By 2014, Entrepreneur wrote that Selfstarter had helped entrepreneurs raise as much as $10 million; TechCrunch called it an open-source do-it-yourself crowdfunding site competing with Kickstarter that startups had used to raise $10 million.⁠[5][2]

On June 5, 2014, he was selected as one of that year’s 20 Thiel Fellows, each of whom received $100,000 over two years to launch their business ideas and had to drop out of college. The list of fellows gives him as 18 and from Lafayette, CaliforniaCaliforniaCalifornia is a U.S. state on the Pacific coast; its capital is Sacramento and its largest city is Los Angeles. California was admitted to the Union on September 9, 1850, as the 31st state. Its population at the 2020 Census (April 1, 2020) was 39,538,223, the largest of any state.Open the full entry, and says that, having built the crowdfunding platform Selfstarter, he would be working to make it easier for anyone to start a business.⁠[5]

TechCrunch wrote on July 8, 2014 that the class’s 20 fellows were all under 20 and had been picked from more than 1,000 applicants, and that a little over half of them (10 boys and a girl) lived together in what appeared to be a giant abandoned building in San Francisco’s Mission, where he was one of the housemates (spelled “Jared Sumner” in the article). The article notes that Selfstarter predated his time in the Fellows house; he viewed the program as a two-year education of sorts and said, “If and when I return to college I can have a new perspective.”⁠[2]

In an interview published by InfoWorldInfoWorldInfoWorld is a technology publication originating in 1978, serving enterprise developers, software architects and technology decision-makers as part of Foundry.Open the full entry in June 2023, he said that he had long wanted to start a company and that “I did the Thiel FellowshipThiel FellowshipThe Thiel Fellowship is a two-year grant program started by investor Peter Thiel and run by the Thiel Foundation that funds young people who skip or stop out of college to build new things instead. The program has been criticized by figures in education for encouraging young people to leave college.Open the full entry in 2014.” The Pragmatic Engineer wrote in September 2023 that he had received the $100,000 grant of the Thiel Fellowship founded by Peter ThielPeter ThielPeter Thiel is an American entrepreneur and investor, a co-founder of PayPal and Palantir Technologies, and the first outside investor in Facebook. He is a partner at the venture capital firm Founders Fund and founded the Thiel Fellowship, which funds young people to leave college and build new things; his public skepticism of higher education, his support for Trump in 2016, and his funding of litigation against Gawker Media have drawn controversy.Open the full entry.⁠[6][7]

He wrote in December 2025 that almost five years earlier he had been building a Minecraft-like voxel game in the browser; as the codebase grew, it took 45 seconds to test whether a change worked, mostly spent waiting for the Next.js dev server to hot reload. In the version recorded by InfoWorld in 2023, it was a multiplayer voxel game in the browser, and the time from saving code in his editor to seeing the change in the browser was about 30 seconds, long enough to instinctively read Hacker News. He recalled on Syntax that he spent about a year building the game, including about three weeks just on how to store the voxel data, which also had to be synced over the network between players as they edited; he also said that in browsers a tab crashes once it uses more than about a gigabyte of memory.⁠[8][6][1]

He wrote that he began porting esbuild’s JSX and TypeScript transpiler from Go to Zig and had a somewhat working transpiler three weeks later; to get Next.js server-side rendering working he needed a JavaScript runtime, and after about a month of reading WebKit’s source code to figure out how to embed JavaScriptCore with the same flexibility as Safari does, he had the very first version of Bun’s JavaScript runtime. He said on Syntax that he experimented with several runtimes before choosing JavaScriptCore, which was the fastest to start up and had a really fast JIT; he described Go as a warm-up toward lower-level memory management, said he first saw Zig on Hacker News, and read its documentation from top to bottom. On JS Party he said that he had tried Rust for a bit but was not very productive with it.⁠[8][1][9]

He wrote that he spent much of that first year in a very cramped apartment in Oakland, just coding and tweeting about Bun. In the InfoWorld interview he said that Bun was not clearly a startup at first, that he just kept expanding its scope, and that he stopped working on the game after getting deeply into Bun.⁠[8][6]

On the name, he said on Syntax, to InfoWorld and on JS Party that it came from a friend’s bunny named Bun, and in the InfoWorld interview he said that the friend suggested it; he recalled on Syntax that at first he did not want to name the project after his friend’s bunny, but came round because the name suited both a bundler and a bundling of many tools of the JavaScript ecosystem, and because he likes cute names and logos. DevClass wrote in 2022 that the name may be an abbreviation of “bundle.”⁠[1][6][9][10]

Anthropic’s 2025 announcement states that Jarred Sumner founded Bun in 2021; DevClass writes that Bun was first previewed in May 2021.⁠[11][12]

In July 2022 he released Bun v0.1.0, an all-in-one bundler, transpiler, runtime (designed as a drop-in replacement for Node.js), test runner and package manager; it gained 20,000 GitHub stars in its first week. DevClass wrote in August 2022 that before the public launch he had spent more than a year building it alone in a private beta (“I spent more than a year building Bun solo in private beta.”); two months after the launch Bun had more than 32,000 GitHub stars and 14,000 Discord members, and the latest release was 0.1.10, with the runtime neither stable nor complete. The code is published on GitHub under the MIT License and depends on the Apple-sponsored JavaScriptCore, which is also used by WebKit, licensed under LGPL v2.⁠[8][13][10]

In August 2022 he announced the company Oven to support and commercialize Bun; DevClass wrote that it had attracted $7 million from the venture capital firm Kleiner Perkins, with some unspecified participation from Guillermo RauchGuillermo RauchGuillermo Rauch is a software developer, entrepreneur and angel investor, and the founder and CEO of Vercel. Originally from Argentina, he was active early in the JavaScript open-source community, co-founded LearnBoost and Cloudup, and worked on projects including Socket.IO, Mongoose and Next.js. He published Smashing Node.js: JavaScript Everywhere in 2012 and in 2015 founded ZEIT, the company later renamed Vercel.Open the full entry, founder and CEO of Vercel. He wrote that the $7 million seed round was led by Kleiner Perkins (thanking Bucky, Leigh Marie and Shrav Mehta in the post), after which he took a salary and convinced a handful of engineers to move to San Francisco to help build Bun. Kleiner Perkins writes that it first met him in 2022, when Bun had just launched v0.1.0, and that it led Bun’s seed round, when the company was called Oven.⁠[10][8][13]

DevClass wrote that he announced Oven’s business model as serverless hosting and continuous integration powered by Bun, in his words “fast serverless hosting and continuous integration for backend and frontend serverless apps,” with a plan to run its own servers on the edge in datacenters around the world, which DevClass took to mean that it would not rely on public clouds. Oven was hiring, mainly for low-level systems programming in Zig and C++, and warned potential employees in a tweet that “Oven is going to be a grind, especially the first nine months or so.” He also set the goal of a stable release of Bun within six months.⁠[10]

In the InfoWorld interview he said that many venture capital firms reached out after seeing developers’ reaction to Bun, and that the name Oven came from the lead investor. On Syntax he said that he thought “Oven” just sounded good.⁠[6][1]

On June 28, 2023, InfoWorld published Matthew Tyson’s interview with him. He said that he still spends too much time coding, which he called his “default happy place.” He was optimistic about Copilot-like language models reducing boilerplate and suggested that future programming languages might be designed for language models; he said he had no opinions on crypto.⁠[6]

On September 8, 2023 he released Bun 1.0 in a post co-signed with Ashcon Partovi and Colin McDonnell, which declared Bun stable and production-ready and set out its aim to eliminate slowness and complexity without throwing away what is great about JavaScript; the post went through what Bun replaces: Node.js, transpilers, bundlers, package managers and testing libraries. The post thanked nearly 300 contributors; at the time the Windows build was “highly experimental,” supporting only the JavaScript runtime, with the package manager, test runner and bundler disabled.⁠[14]

Gergely Orosz of The Pragmatic Engineer wrote on September 22, 2023 that Bun was mostly built by him and that, although it had other contributors, he wrote the lion’s share of its code; that Oven had raised more than $7 million, which let it pay all its contributors a market-rate salary plus equity; and that VercelVercelVercel is a cloud application development and deployment company founded by Guillermo Rauch in 2015 as ZEIT. It contributes to the open-source React framework Next.js and provides application hosting, deployment and runtime services; its products later expanded to AI SDK, v0 and infrastructure for AI applications. The company adopted its current name in 2020 and raised a $300 million Series F in 2025.Open the full entry, ReplitReplitReplit is a software development platform co-founded by Amjad Masad and Haya Odeh, offering browser-based programming, collaboration, application deployment and AI agents. Its early products supported online programming and education before expanding into creating, running and publishing applications through natural language. Incorporated in 2016, the company is headquartered in Foster City, California, United States.Open the full entry, Ruby on Rails and Laravel Sail had added support for Bun. The article quotes the YouTuber and tech investor Theo Browne as saying that most of Bun’s code comes from the same person who makes most of the company’s business decisions, and that “Jared’s done an incredible job of managing this thus far: but he’s mostly done this by working absurd amounts of time.”⁠[7]

After the Bun 1.0 release he said on Changelog’s JS Party episode 295 that the company had seven people, most of them engineers, that “7 million is correct,” and that at the current burn rate it had several years of runway; the company held one meeting a week. He said the next six to twelve months would focus on adoption, after which the plan was to offer hosting built into the runtime, and that Bun had to be permissively licensed. He said the company was hiring C, C++ and Zig engineers and that he spent a lot of time interviewing, that he needed to be faster at reviewing pull requests, and that “I’m not good yet managing my time.” He also said the Windows build was then “really buggy” and that the team would soon spend much more time on it.⁠[9]

Bun 1.1 was released on April 1, 2024, adding support for Windows; he wrote that until then people had asked every day when Bun would support Windows.⁠[15][8]

He wrote that in late 2024 AI coding tools went from “cool demo” to “actually useful,” that he started using Claude Code himself and got “kind of obsessed” with it, and that, as of his December 2025 post, the GitHub username with the most merged pull requests in Bun’s repository over the previous several months was a Claude Code bot, which the team had set up in its internal Discord and mostly used to help fix bugs. He wrote that Claude Code, FactoryAI, OpenCode and others were built with Bun, whose single-file executables turned out to be perfect for distributing command-line tools; the Kleiner Perkins post likewise says that Bun’s single-file executables were perfect for distributing AI coding agents.⁠[8][13]

Bun 1.2 was released on January 22, 2025. He wrote that it improved Node.js compatibility and added built-in PostgreSQL and S3 clients, and that companies including X and Midjourney used Bun in production, while Tailwind’s standalone command-line tool was built with it.⁠[15][8]

Bun 1.3 was released on October 10, 2025, adding a built-in frontend dev server and Redis and MySQL clients, with several improvements to bun install and improved Node.js compatibility. He wrote that Bun’s monthly downloads grew 25% in October 2025, passing 7.2 million.⁠[15][8]

On October 28, 2025, he and a co-author announced on the Bun blog that Vercel now supported the Bun runtime.⁠[15]

On December 2, 2025 he announced in the Bun blog post “Bun is joining Anthropic” that Bun had been acquired by Anthropic, which was investing in Bun as the infrastructure powering Claude Code, the Claude Agent SDK and future AI coding products. He wrote that “Claude Code ships as a Bun executable to millions of users” and that “If Bun breaks, Claude Code breaks.” Anthropic’s announcement page, dated December 3, 2025, says that Anthropic “is acquiring” Bun to further accelerate Claude Code.⁠[8][11]

He wrote that a few weeks earlier he had gone on a four-hour walk with a member of the Claude Code team (named only as “Boris” in the post), and then did the same with many of Anthropic’s competitors; he wrote that he thought Anthropic was going to win and that “Betting on Anthropic sounded like a more interesting path.” He wrote that “Today, Bun makes $0 in revenue,” that the default answer to how Bun would make money had always been an eventual cloud hosting product vertically integrated with Bun’s runtime and bundler, and that the company had more than four years of runway to figure out monetization, but that joining Anthropic let it skip that chapter entirely and focus on building the best JavaScript tooling, with long-term stability and more resources, and with the team hiring engineers. He argued that if most new code is going to be written, tested and deployed by AI agents, the runtime and tooling around that code become far more important.⁠[8]

He wrote that what would not change was that Bun stays open source and MIT-licensed, continues to be very actively maintained by the same team, is still built in public on GitHub, and keeps a roadmap focused on high-performance JavaScript tooling, Node.js compatibility and replacing Node.js as the default server-side runtime for JavaScript; what would change was that the team would help make coding tools such as Claude Code and the Claude Agent SDK faster and smaller, get an earlier look at where AI coding tools are heading, and ship faster.⁠[8]

Anthropic’s announcement states that Bun had more than 7 million monthly downloads and over 82,000 GitHub stars and had been adopted by companies such as Midjourney and Lovable; that Anthropic had been a close partner of Bun for many months, that their collaboration directly drove the launch of Claude Code’s native installer, and that Bun had been key in helping scale Claude Code’s infrastructure; that Claude Code, which became generally available in May 2025, reached $1 billion in run-rate revenue in November, six months later; and that Bun will remain open source and MIT-licensed. Mike Krieger, Anthropic’s Chief Product Officer, said in the announcement, “Bun represents exactly the kind of technical excellence we want to bring into Anthropic,” and that “Jarred and his team rethought the entire JavaScript toolchain from first principles.”⁠[11]

Leigh Marie BraswellLeigh Marie BraswellLeigh Marie Braswell is a venture capitalist and partner at Kleiner Perkins who invests mainly in infrastructure and artificial intelligence application startups; she was an early engineer and the first product manager at Scale AI and began her investing career at Founders Fund.Open the full entry of Kleiner Perkins published “Celebrating Bun” the same day, writing that Bun remains open source, MIT-licensed and built in public, now with the resources of a world-class AI lab behind it. DevClass wrote on December 3, 2025 that Bun’s native code is written in Zig, which is far from mature, its current version then being 0.15.2, and whose creator, Andrew Kelley, has a strict no-LLM, no-AI policy in the code of conduct for Zig contributors; DevClass saw possible friction if developers now at Anthropic turned to contributing to Zig, and judged that Bun, until then driven by his intense personal drive, seemed bound to see some change of direction under new ownership.⁠[13][12]

In the post “Rewriting Bun in Rust,” published on July 8, 2026, he wrote that he rewrote Bun in Rust using about 50 dynamic workflows in Claude Code run continuously over 11 days, from May 3 until the merge on May 14; at peak four workflows ran at once, each in a separate worktree with 16 Claudes per workflow, about 64 Claudes at a time. He wrote that he used a pre-release version of Claude Fable 5 for much of the rewrite, and that he began with just three files before asking Claude to translate all 1,448 .zig files to .rs files. Excluding comments, he wrote, Bun was 535,496 lines of Zig, and the rewrite replayed 6,502 commits (merges excluded); a team of engineers with full context on the codebase would have needed a year of work, and before the merge it took 5.9 billion uncached input tokens, 690 million output tokens and 72 billion cached input token reads, around $165,000 at API pricing.⁠[16]

He explained that Bun started as a line-for-line port of esbuild’s JavaScript and TypeScript transpiler from Go to Zig and that “Zig made Bun possible,” but that, JavaScript being a garbage-collected language, correctly handling the lifetimes of garbage-collected and manually managed values in Bun had been a major source of stability issues, mostly small memory leaks and occasionally crashes; a large share of those bugs were use-after-free, double-free and “forgot to free” in an error path, which are compiler errors in safe Rust. He wrote that the team had patched the Zig compiler to add Address Sanitizer support, but would still rely on style guides enforced through code review, and that even with ASAN memory corruption and leaks would still happen; enforcing code style was their best bet for the stability issues, and they had added Rust-inspired smart pointers to Bun’s codebase for it; he wrote, “But honestly, I didn’t want to do it.” Homegrown smart pointers, he wrote, offered worse ergonomics than Rust with none of the guarantees, so he decided to spend a week testing whether Anthropic’s new model could rewrite Bun in Rust. The post states that Claude Code v2.1.181 (released June 17) and later versions use the Rust port of Bun; his conclusion was that “One engineer can do a lot more today than a year ago.”⁠[16]

Stephen O’Grady of the analyst firm RedMonk wrote on June 4, 2026 that Anthropic had acquired Oven, the maker of Bun, in early December of the previous year; that bot-authored commits had exceeded half of the project’s commits as early as the previous August and after the acquisition rarely fell below that share, peaking above 80%; and that a month earlier he had said on Twitter, “We haven’t been typing code ourselves for many months now.” RedMonk wrote that Bun’s monthly npm downloads grew sixteenfold, from 445,000 to 7.3 million, in under 30 months, that the total number of human contributors to the project had fallen to roughly half of what it was, and that of about seven identifiable pre-acquisition Oven employees at least four had clearly departed or stopped contributing. RedMonk’s assessment is that three of the four promises in the acquisition announcement, on the MIT license, active maintenance and building in public on GitHub, had been kept, but that the team appeared to have gone its separate ways.⁠[17]

On August 20, 2026 he released Bun 1.4 in a post co-signed with four other authors, the first version of Bun written in Rust; he had written that v1.3.14 was the last version written in Zig, that so far v1.4.0 fixed 128 bugs that reproduce in v1.3.14, and that, with the Rust rewrite, ICU changes and identical code folding combined, Bun’s binary shrank by about 20% on Linux and Windows.⁠[15][16]

As of November 2026, his personal website states that he works on Bun and Claude Code at Anthropic, and his GitHub profile gives his location as San Francisco. The footer of Bun’s official website says that Bun is “Now part of Anthropic,” with the copyright held by Anthropic, PBC.⁠[3][18][19]

His personal website, after describing his creation of Bun and his work at Anthropic, says that before that he was a frontend engineer at Stripe, and that long before that he was a Thiel Fellow; The Pragmatic Engineer called him a former Stripe engineer in 2023. He said on Syntax and to InfoWorld that he had spent more time as a frontend engineer than on systems work, and on JS Party that much of his inspiration for Bun came from his experience as a frontend engineer using Node.js-based tools.⁠[3][7][1][6][9]

He wrote that after Bun 1.0, as production usage started to pick up, the company raised a $19 million Series A led by Khosla VenturesKhosla VenturesKhosla Ventures (KV) is an American venture capital firm founded in 2004 by Vinod Khosla, the founding CEO of Sun Microsystems, and headquartered in Menlo Park, California. It made heavy early bets on clean technology, became OpenAI’s first venture capital investor in 2019, and its portfolio also includes companies such as DoorDash, Block (formerly Square), Impossible Foods, and Rocket Lab.Open the full entry (thanking Nikita and Jon in the post), grew the team to 14 people and moved into a slightly larger office. DevClass wrote in December 2025 that he said the company behind Bun had raised $26 million in venture capital.⁠[8][12]

He said on Syntax that he had long been frustrated by how long everything takes, especially on the frontend side, and often browsed Hacker News while waiting for things to build; that he often tweets about the various performance improvements made by the WebKit/Safari team; and that he tends not to use linters much but uses Prettier a lot.⁠[1]

Personal website: https://jarredsumner.com/ (opens in a new window).⁠[3][18]

X: Public account: https://x.com/jarredsumner (opens in a new window).⁠[3][18]

GitHub: Public account: https://github.com/Jarred-Sumner (opens in a new window).⁠[3][18]

Bun: Official website: https://bun.com/ (opens in a new window).⁠[19]

Thiel Fellowship: Official website: https://thielfellowship.org/ (opens in a new window).⁠[20]

Stripe: Official website: https://stripe.com/ (opens in a new window).⁠[21][3]

Anthropic: Official website: https://www.anthropic.com/ (opens in a new window).⁠[11]