If you are talking about async/await:

- for concurrency it has been in the standard library for a couple of years. Also you can implement it as a library without compiler support.

- for parallelism, Rust is in advance. Nim has a simple threadpool with async/await (spawn/^), it works but it needs a revamp as there is no load balancing at all.

You can also fallback on the raw pthreads/windows fibers and/or OpenMp for your needs or even OpenCL and Cuda.

Regarding the revamp you can follow the very detailed Picasso RFC at https://github.com/nim-lang/RFCs/issues/160 and the repo I'm currently building the runtime at https://github.com/mratsim/weave.

Obviously I am biaised as a Nim dev that uses Nim for both work and hobby so I'd rather have others that tried both comment on their experience.