This is one of the things that I'm also looking on at Zig like a slow moving car crash about: they claim they are memory safe (or at least "good enough" memory safe if you use the safe optimization level, which is it's own discussion), but they don't have the equivalent to Rust's Send/Sync types. It just so happens that in practice no one was writing enough concurrent Zig code to get bitten by it a lot, I guess...except that now they're working on bringing back first-class async support to the language, which will run futures on other threads and presumably a lot of feet are going to be fired at once that lands.

IIUC even single-threaded Zig programs built with ReleaseSafe are not guaranteed to be free of memory corruption vulnerabilities; for example, dereferencing a pointer to a local variable that's no longer alive is undefined behavior in all optimization modes.

Zig's claims of memory safety are a bad joke. Sure, it's easier to avoid memory safety bugs in Zig than it is in C, but that's also true of C++ (which nobody claims is a memory safe language).