A contractor employed for just this purpose recently leaked over 1000 recordings that came from Google Assistant. Some of these recordings revealed that Google Assistant did occasionally record when no one spoke the wake word.
…But the most disturbing part is that a contractor could leak these voice transcripts in the first place. It’s not clear how they managed to copy the data, and Google says it’s now investigating and plans to find the leaker. Hopefully, along the way, they add more security precautions that prevent removing data from its servers.