From the maintainer: https://drewdevault.com/blog/Forking-vim/

HN discussion: https://news.ycombinator.com/item?id=47519308

With respect to the creator, Vim9 script is inferior to Lua in terms of adoption, learning curve, stability, features and probably performance. If the purpose is to serve users a new DSL is not really defensible when Neovim has proved Lua works

I only noticed it when a slew of security holes (re-)introduced by uncritical merging of LLM code got CVEs assigned.

Luckily I was lazy running a custom build of vim and hadn't updated since they started lowering the merge barrier (or however you can put this politely).