Google is about to update phones with Android 6.0 or higher with google assistant. As it stands now the update will arrive next week via the google services update in the play store.
“The Google Assistant will begin rolling out this week to English users in the U.S., followed by English in Australia, Canada and the United Kingdom, as well as German speakers in Germany. We’ll continue to add more languages over the coming year.
The Google Assistant will automatically come to eligible Android phones running Nougat and Marshmallow with Google Play Services. You’ll also see the Google Assistant on some newly announced partner devices, including the LG G6.”