This had been announced back in September 2015, albeit from a Google Docs for Education point of view:
https://googleblog.blogspot.co.nz/2015/09/google-docs-classr...
Under the first video, see "With Voice typing, you can record ideas or even compose an entire essay without touching your keyboard."
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It seems that what's new are the "Voice commands" to Select Text, Format, etc. etc. That's really great! Take a look at the commands here: