Anthropic has acquired Bun, the popular JavaScript and TypeScript runtime and toolchain. The company says the deal strengthens the infrastructure behind both its coding tool Claude Code and the Claude Agent SDK. Bun already powers these systems today, and Claude Code ships to millions of users as a Bun executable.
Anthropic also highlighted a major milestone: in November 2025, just six months after its public launch in May, Claude Code reached an annualized revenue of one billion dollars.
Bun founder Jarred Sumner emphasized that Bun is essential to Claude Code’s stability and performance. In his announcement of the deal, he explained that Anthropic has a direct interest in keeping the runtime fast, stable, and reliable because Claude Code depends on it.
How Bun shapes the next phase of AI-driven software development
Sumner created Bun in 2021 as an all-in-one developer toolkit that combines a runtime, package manager, bundler, and test runner. It has developed a reputation for being significantly faster than established alternatives like Node.js.
Anthropic views Bun’s speed and architecture as critical for the next stage of AI-driven development. As more AI agents write, test, and execute code, the demands on the underlying runtime continue to evolve.
According to Sumner, Bun was designed to make developers more productive, and modern AI coding tools follow a similar path. Bun’s ability to bundle applications into single-file executables that run anywhere without a preinstalled runtime makes it especially well-suited for distributing AI agents.
Mike Krieger, Anthropic’s Chief Product Officer, described Bun as a prime example of technical excellence and said Anthropic wanted the project in-house to keep pace with rapidly growing AI adoption.
Why staying open source beats chasing a business model
For the Bun team, the acquisition resolves a long-standing monetization challenge. Despite raising 26 million dollars from venture firms like Kleiner Perkins and Khosla Ventures, Bun had not generated revenue.
The startup still had enough funding to operate for four more years, but the founders decided not to build a cloud hosting business simply to earn money. Sumner explained that joining Anthropic allowed the team to skip the pressure to create a business model and instead focus on the technology.
He also noted that several other companies had expressed interest in acquiring Bun, but ultimately he concluded that "Anthropic is going to win."
Bun will remain open source under the MIT license, with ongoing development continuing publicly on GitHub.
