This is preposterously ambitious - a complete Rust re-implementation. Looks like it's mostly claude?

Yeah, this is pretty much a textbook example of what AI agents make possible these days: things that are ridiculously ambitious, but aren't conceptually very difficult (or, at least, are conceptually well-trodden ground). Things like emulators, language runtimes, platform reimplementations like Darling, etc.

JITting Rust isn't conceptually very hard: you just take rustc and make everything dynamic instead of static. The only thing that was stopping it before was the sheer amount of effort. Well, now we have a way to reduce that effort.

Yea it's claude+codex over the course of a month. It definitely isn't a one shot.