If anyone is interested in digging a bit deeper into this.

"Progress report of 'Ruby 3 Concurrency'" (2018) http://atdot.net/~ko1/activities/2018_RubyElixirConfTaiwan.p...

"Parallel programming in Ruby3 with Guild" (2018) http://atdot.net/~ko1/activities/2018_rubyconf2018.pdf

"Ruby 3 Concurrency" (2016) http://atdot.net/~ko1/activities/2016_rubyconf.pdf

A bit off-topic but still interesting, it talks about the goal of reaching over 100k threads to support a massive network of concurrent connections. "MaNy Project" (2022) http://atdot.net/~ko1/activities/2022_rubykaigi2022.pdf