Anthropic just bought your favorite JS runtime...

Updated: December 8, 2025

Fireship


Summary

Anthropic's acquisition of Bun, a JavaScript and TypeScript toolkit, surprised the industry. The creator, a high school dropout, developed Bun to address slow JavaScript tools and secured significant funding. Bun's focus on compiling apps efficiently aligns well with Anthropic's AI environment, potentially paving the way for AI agents to handle new code. The tech community hopes Bun will remain open-source post-acquisition, but concerns linger about Anthropic's approach to such projects. Educational platforms like Brilliant may help navigate any transitions in the future.


Unexpected Acquisition of Bun by Anthropic

Anthropic, the AI research company, acquired Bun, the JavaScript and TypeScript toolkit, surprising many in the industry. The acquisition was completed by a member of Claude Code's technical staff, not the typical software engineering route.

Origin Story of Bun

The origin of Bun dates back to 2021 when initial tweets gained traction due to frustrations with slow JavaScript tools. The creator, a high school dropout, spent a year developing Bun to address these issues, leading to a significant seed round from Kleiner Perkins.

Bun's Development Progress

Bun was officially announced a year later and has since improved its tools and clients to become a prominent player in the JavaScript ecosystem with high monthly downloads and AI-compatible primitives.

Bun's Alignment with AI Future

Bun's focus on compiling apps efficiently aligns with Anthropic's AI environment, suggesting a potential direction where AI agents may handle new code. This synergy makes Bun valuable infrastructure for companies like Claude Code.

Future of Bun under Anthropic

While fans hope Bun will remain open-source and supported by the same team post-acquisition, there are concerns about Anthropic's approach to open-source projects. The tech community has seen beloved tools deprecated before, emphasizing the need for solid educational resources like Brilliant to navigate such transitions.


FAQ

Q: What is Bun?

A: Bun is a JavaScript and TypeScript toolkit developed to address frustrations with slow JavaScript tools.

Q: Who acquired Bun?

A: Anthropic, the AI research company, acquired Bun.

Q: What is the origin of Bun?

A: The origin of Bun dates back to 2021 when initial tweets gained traction due to frustrations with slow JavaScript tools.

Q: What is the focus of Bun?

A: Bun's focus is on compiling apps efficiently, aligning with Anthropic's AI environment.

Q: What significant event occurred a year after Bun's development?

A: A significant seed round from Kleiner Perkins was secured by Bun a year after its development.

Q: Why are fans concerned about Anthropic's approach to open-source projects?

A: Fans are concerned about the potential for Bun to deviate from being open-source and supported by the same team post-acquisition.

Q: What are the concerns in the tech community regarding tools like Bun?

A: The tech community has seen beloved tools deprecated before, emphasizing the need for solid educational resources like Brilliant to navigate such transitions.

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