As I read in news about the update(take and share screenshot) for google assistant but that update only for pixel devices, not for nonpixel devices.
I don't try it yet but probably it should work
Download the Google Play Services APK compatible with your device from here. There will be three files in the zip folder. Install the one (arm for Android 5.0+, arm for Android 6.0+, arm64+arm for Android 6.0+) compatible for your device.
Copy the file over to your Android phone. Remember, it needs to be running at least Android 6.0 or up in order for this to work.
Head on over to Settings > Security and tick the box beside Unknown sources, allowing for apps to be installed from outside the Google Play Store.
Using your favorite file manager, locate the APK and tap it before following the installation prompts.
Marvel at your all-new Google Assistant.
after updating it, google play service will bring Google Assistant updates for you
ou will get further Explanation on this link. If this link disappear for some reason then just follow the above steps to get things done.