From DHH's long-winded keynote at Rails World 2026. He was bragging that Hey's backend is so efficient because it's written in Rust (which he hates and refuses to read).
I remember when HEY first came out, I got to try it and thought it was kinda useless. Defining an entire email service by the removal of one step from any other email service seems silly. (Coming from a guy who’s actually written a unique email service.)