Sandstorm.io doesn't use protobuf, it uses Cap'n Proto, which was designed to replace protobuf.
Fun fact: The Zanzibar project was started in ~2011 specifically to replace my main project at the time, which was trying to solve the same problems. Apparently, some senior engineers felt letting me work on core infrastructure was too dangerous. They succeeded in turning my project into a lame duck and making me quit, which is when I then started working on Cap'n Proto and Sandstorm.io. In retrospect I'm glad it happened.
Yeah... Google is not always the most fun place to work on big infrastructure projects.