Kio is based on polymorphic lambda calculus with higher-kinded types. Kio has type-driven macros (elaborators) and it can statically check asserted equivalences using a normalizer.
Kio is a minimalistic language. It doesn't have built-in effectful functions and it doesn't even have built-in string or numeric types. Instead programs declare the capabilities they need and the host supplies them.
The language is designed with AI, which is bound to raise some eyebrows, so I blogged about that here: https://jdevuyst.github.io/kio/blog/2026-10-01-introducing-k...