Considering it's going to consume libghostty, I'm betting it'll be Zig.

The application layer is in Swift at least.

libghostty exports a C ABI. For an application from Mitch at this layer I would guess Go.

Mitch said he doesn't like go since they added generics.

I checked the available jobs and they are hiring Typescript for web, Go for infrastructure,systems, Objective-C, swift for Apple

I dig the ssh jobs page, UX is very good.