>It can often outperform hand-optimized Rust in worst-case parallel workloads (p99), despite Rust having a number of pretty huge advantages...

I will say this comes with the asterisk that it heavily depends on what your concurrent system/problems looks like!

...but more often than not when dealing with web problems and network IO, the shape of concurrency/parallelism I need looks exactly like Goroutines, and even as someone who uses Rust/tokio daily: the Go runtime is an incredibly engineered system that usually beats Rust in my experience for application dev tasks.

Anyways, I love Crystal's syntax around concurrency! I wish we lived in a world where it had tons of Google engineers optimizing the runtime :)