Anthropic Acquires Bun in Surprise Move, Reshaping AI and JavaScript Tooling Landscape

On December 5, 2025, the tech world was surprised by the unannounced acquisition of Bun, the all-in-one JavaScript and TypeScript toolkit, by AI research giant Anthropic. Bun, initially conceived by Jared Sumner in 2021 out of frustration with slow JavaScript build times, quickly gained traction for its innovative approach, notably porting ESBuild’s JSX and TypeScript transpiler from Go to Zig. This led to its evolution into a comprehensive toolkit, offering a bundler, transpiler, runtime, test runner, and package manager. Following a $7 million seed round from Kleiner Perkins, Bun launched version 1.0 in 2023, added Windows support in 2024, and has since grown to over 7 million monthly downloads and 83,000 GitHub stars, establishing itself as a beloved and high-performance tool in the developer ecosystem.

Anthropic’s strategic interest in Bun stems from its critical primitives for AI development. Bun’s core strengths—speed, predictability, and the ability to compile applications into a single, compact executable—make it an ideal foundation for building high-performance CLIs, a critical component for AI agents like Anthropic’s Claude Code. This acquisition suggests Anthropic’s intent to invest deeply in the infrastructure powering its AI products. While the Bun team has committed to maintaining its open-source, MIT-licensed status and continued public development under the same team, concerns arise given Anthropic’s historical stance on open source, exemplified by Claude Code itself not being open source. The tech community is now watching closely to see how this merger will balance Bun’s commitment to its developer base with Anthropic’s strategic AI objectives.