He says that “almost every aspect of X” has been rebuilt while he was head of product, including its timeline, Android app, chat, and notifications. Going forward, the “next leaders” mentioned are Benji Taylor leading design with iOS lead Jonah Katz and Mridul Singhai leading the product team.
Bier previously co-founded the startups tbh (acquired by Meta) and Gas (acquired by Discord). He was appointed to lead product just days before former X CEO Linda Yaccarino stepped down, and has been a public face of the company ever since.