Simon Willison’s Weblog

Anthropic acquires Bun. Anthropic just acquired the company behind the Bun JavaScript runtime, which they adopted for Claude Code just in July. Their announcement includes an impressive revenue update on Claude Code:

In November, Claude Code achieved a significant milestone: just six months after becoming available to the public, it reached $1 billion in run-rate revenue.

Here "run-rate revenue" means that their current monthly revenue would add up to $1bn/year.

I've been watching Anthropic's published revenue figures with interest: their annual revenue run rate was $1 billion in January 2025 and had grown to $5 billion by August 2025 and to $7 billion by October.

I had suspected that a large chunk of this was down to Claude Code - given that $1bn figure I guess a large chunk of the rest of the revenue comes from their API customers, since Claude Sonnet/Opus are extremely popular models for coding assistant startups.

Bun founder Jarred Sumner explains the acquisition here. They still had plenty of runway after their $26m raise but did not yet have any revenue yet:

Instead of putting our users & community through "Bun, the VC-backed startups tries to figure out monetization" – thanks to Anthropic, we can skip that chapter entirely and focus on building the best JavaScript tooling. [...] When people ask "will Bun still be around in five or ten years?", answering with "we raised $26 million" isn't a great answer. [...]

Anthropic is investing in Bun as the infrastructure powering Claude Code, Claude Agent SDK, and future AI coding products. Our job is to make Bun the best place to build, run, and test AI-driven software — while continuing to be a great general-purpose JavaScript runtime, bundler, package manager, and test runner.