The article says nothing about them switching to rust. They implemented a specific data structure in rust using elixir NIFs (native interface). This is equivalent of calling a C library from other languages.

"Our core services aren’t written in Rust, they are Elixir-based."

They haven't switched, just use Rust at some places for performance improvements.

My bad, I visibly remembered the article incorrectly and didn’t take the time to read again when sharing.

Thanks for the correction. Unfortunately I cannot edit my original comment.

Others have already repeatedly mentioned this was a performance optimization. Elixir/Erlang is not particularly good for heavily CPU bound tasks--This is by design. For lack of a better source, here is a post on the Elixir forum from Robert Virding (one of the creators of Erlang) on the subject: https://elixirforum.com/t/on-why-elixir/34038/62

Based on article they didn’t switch to Elixir but instead are using Rust within Elixir in order to solve complex performance issues.