During CES, Google made an announcement regarding Google Assistant and its future in the world. Google outlined many new ways Google Assistant would be able to help you throughout the day in various areas. One area that stood out was in the car, in its announcement, Google stated that Google Assistant would be making it's way to your car to help you with your voice commands while driving.
This is a little confusing, I thought that Google Assistant was always available in Android Auto. This is wrong, it seems that Android Auto was using a simpler voice search method with the implementation it had built in. Every time you would say "OK Google" to your car it would trigger an implementation based on Voice Search instead of Google Assistant.
Now that Google Assistant is coming to Android Auto there will be a wider range of functions which users will be able to access through voice commands. Here is a video showing Google Assistant working in Android Auto:
Many of the voice commands which are usually only accessible through Google Assistant worked on Android Auto before the new integration of Google Assistant, Android Auto would even use the same animation as Google Assistant, which is what really made people think they already had Google Assistant.
With the new integration of Google Assistant, we will be able to access more in-depth functions. You should be able to do all the things you can do with your Android phone such as control external hardware such as lights, and access specific apps such as Spotify to play a playlist. Everything in this update will be an added feature, so you can keep using Android Auto as you already did or step it up and go further.