Google Assistant is getting a slight redesign on iOS, some other improvements too3
Basically, Google has decided to slightly redesign Assistant on iOS devices giving the app a rounder, cleaner look. Some colors have been changes here and there, but that's about all the visual changes that have been introduced in this update.
As per Google's changelog, many bugs have been squashed and some stability improvements have been included in the update too. There aren't any new features introduced, so don't go looking for any.
It's worth mentioning that this particular update should arrive on Android devices as well, but we don't have a clear ETA for this one yet. Aside from the visual changes that include a rounder interface, Android users may get a few other improvements, but we'll just have to wait and see.