https://www.trains.com/trn/news-reviews/news-wire/first-u-s-hydrogen-powered-trainset-enters-phase-ii-of-testing-in-california/

Entered service in 2024. https://www.sfgate.com/travel/article/california-train-zemu-debut-san-bernardino-19664920.php

It's a Stadler FLIRT (Fast Light Innovative Regional Train, German: Flinker Leichter Innovativer Regional-Triebzug) made by Stadler Rail of Switzerland.

https://en.wikipedia.org/wiki/Stadler_FLIRT