*The Rustification of Bun#
Rewriting 500,000 lines of Zig into another language would be a gargantuan undertaking if done by hand. “A rewrite in another language would take a small team of engineers a full year. It would mean freezing bugfixes, security fixes or feature development for that time,” Sumner wrote.
Instead, Sumner went with Claude. He spun up about 50 dynamic Claude Code workflows, reaching a peak of about 1,300 lines of code per minute and generating over a million lines of Rust code. The job took 11 days and cost about $165,000 at API pricing. Claude Fable did most of the heavy lifting.
Kelley does indeed blame Sumner’s poor engineering and lays out a series of events where he describes a transformation into VC-backed startup and the changes in engagement with Zig, and also the effect this has on Bun’s source. I’m inclined to believe Kelley’s accounting. Let’s not forget that it was Sumner/Anthropic that decided to throw Zig under the bus first.