epic games' language in development is referenced here in this presentation

   https://youtu.be/VBT0j14rn5c

I think Rust's concurrency safety (e.g. async on a single thread) is mostly granted by the Pin trait [1], and the async code-gen making sure lifetimes make sense over .await points (which requires things to be either pinned across those points, or to not care about their location in memory potentially moving).

Thread safety is instead given by a couple of auto-derived marker traits, called Send and Sync [2], that denote which kinds of data can be sent or shared between threads safely.

This is coupled with types like Arc, Mutex, etc that can wrap data that isn't safe to share, so that the wrapped data as a whole is safe to share. It is also coupled with functions (like std::thread::spawn [3] and MPSC's send()) that have a requirement for the data to either be Sync/Send, or to take full ownership of it (which ensures there are no other active references to it).

[1] https://doc.rust-lang.org/std/pin/struct.Pin.html

[2] https://doc.rust-lang.org/std/marker/trait.Sync.html

[3] https://doc.rust-lang.org/std/thread/fn.spawn.html