[pasttense01]

From the Wall Street Journal:

"The company said Friday that it is promoting its chief technology and operating officers, Dmitri Dolgov and Tekedra Mawakana, to lead a decade-old effort to make self-driving cars a reality. They will share the title of co-chief executive... Mr. Dolgov is one of the founders of Google’s self-driving car project. He joined the program when it began in 2009 and led the development of Waymo’s autonomous system, known as Waymo Driver. He studied physics and math at the Moscow Institute of Physics and Technology before earning a doctorate in computer science from the University of Michigan. As chief operating officer, Ms. Mawakana has led the effort to commercialize Waymo’s self-driving system. She has a law degree from Columbia University and previously worked at other tech companies such as eBay Inc. and Yahoo."

https://www.wsj.com/articles/waymo-ceo-john-krafcik-is-leavi...

My guess it that traditionally the chief operating officer would have been promoted and the chief technology officer would stay as the chief technology officer--but that there was a significant risk of the chief technology officer leaving if he wasn't promoted. So you end up with co-CEOs.