Bun's Migration from Zig to Rust as a Potential Case Study for Gradual Disempowerment

TL;DR:Bun is a very large and very influential open-source project. It is being migrated from the easier-to-read Zig programming language to harder-to-read but memory-safe Rust. This is done almost entirely by the AI tool Claude Code. The migration may become one of the earliest major case studies of human control over a significant software project becoming increasingly indirect--both due to the nature of the programming language itself and LLM-generated code being quite convoluted.What happened?On May 14 2026, a Rust version of Bun was merged to the "main" branch of the Bun repository[1].Bun was originally written in Zig, by humans. Then they started to use AI coding tools, likely with an increased intensity after their acquisition by Anthropic in December 2025[2].Jared Sumner, Bun's creator, posted that the Zig version will be discontinued in favor of the Rust version. Why is this a big deal?As far as I'm aware, this is the first example of a hand-written large open-source software project entirely transitioning to LLM-written code.According to what Jarred Sumner says on X, they haven't been typing code themselves, even before the acquisition--in other words, Claude was already Bun's de facto primary coder.An explosion of complexity"An idiot admires complexity, a genius admires simplicity."— Terry A. DavisAn initial bad sign about the viability of human maintenance is the increased codebase size. After the migration, the code size increased to over 1 million lines of Rust, compared to ~600,000 lines of the previous Zig code. This is especially surprising given that Rust is usually the more concise of the two: Zig is more verbose and will usually require more LoC than Rust for the same high-level task. This implies that this explosion of complexity is largely a result of Claude use.To put things into scale, let's compare this with some other important OSS projects:JavaScriptCore: ~810k lines (this is the JavaScript compiler Bun is wrapping!!)SQLite: ~400k linescUR