Google officially announced this new feature in this years Google I/O 2017 developer event. You will see this feature in your phone once your launch Assistant on your phone.
To check that you got this feature or not, simple open the app and check the keyboard icon at the bottom left in the screen. The feature will be active when you say "OK Google", or at the tap or long press on home button.
I got this update in my Nexus 6p, Below is the screenshot of the new feature.
Download the APk file from below link:
Google Assistant APK