ExpressJet Airlines made this announcement:
On August 24th, ExpressJet reached a major milestone by successfully demonstrating a flight under Part 121 for the FAA. After a few administrative items are completed, ExpressJet will receive full FAA approval to conduct revenue operations under its 121 certificate.
Source: https://worldairlinenews.com/2021/08/30/expressjet-is-close-to-receiving-its-part-121-aoc/