It seems Google is rolling out the design changes in Google Assistant to non-Pixel devices already. Some of the changes that Google announced back in October are coming out to other devices.
This time, the Assistant covers up only half of the display, instead of the entire screen. In fact, you also get the underlined style of Google Assistant just like Siri on Apple.
Other than that, you also get a transparent background, which means, the screen content behind the Assistant is visible instead of getting blurred.
However, only few people are getting this u[ate. it seems Google is testing the updates before releasing it to the public. You may get this feature sometime in the near future.