In December 2025, Anthropic bought Bun, the JavaScript runtime with over 22 million monthly downloads, and then ported its entire codebase from Zig to Rust. The port was done in 11 days by 64 parallel Claude agents at a reported cost of $165,000 in tokens. Those numbers have traveled far, usually attached to a prediction: frontier AI providers will one day charge real per-token rates for software development, and developers who can still read code will become rare specialists.
The core facts check out. The conclusions deserve a harder look, because the $165K figure is narrower than it sounds, the process was not hands-off, and the model that did the work is not one you can buy. Here is what the sources actually say.
What actually happened
The primary source is Jarred Sumner's own engineering write-up, Rewriting Bun in Rust, published July 8, 2026 on the Bun blog. The verified facts from it:
Anthropic acquired Bun in December 2025. Sumner and the Bun team now work at Anthropic.
