Much like all of the rest of Google's apps, the actual Google app is one which has seen quite a few updates of late and it now seems to be in the process of receiving the latest one. However, unlike some of the more recent updates, it does seem at the moment that this one is more of an aesthetic update than a functional one. In terms of what's new, the details are quite light. However, one feature which does seem to be included in the update is a change in the way you wait for Google Now on Tap to present content. Prior to the update, when Google Now on Tap was enabled, the user would typically see a blue spinning wheel icon which would advise that the content was loading. This has now gone completely and instead a new animation appears while you are waiting. The new animation is essentially a carousel animation which cycles between various icons including the search icon, location icon, movies icon, music icon and a dining icon. Essentially, highlighting the uses that Google Now on Tap provides. You can see an example of one of the icons in the image below.
As mentioned, details on what else is included in the update are extremely minimal at the moment. However, a teardown of the app has revealed that Google is likely to introduce a new feature which lets users donate their screenshots. The idea being that by letting Google see your screenshots, they might be able to help improve the Now on Tap service. From the currently known details, this does seem to be an optional feature, so you will be able to opt out if you do not want to let Google peek at your screenshots.
In terms of the update, this is one which is said to have started rolling out yesterday so there is a good chance that you have already seen the update arrive on your device. If you haven't and would rather push the update to your device, then you can by downloading the update though the link below. For reference, the update comes in just under 30 MB.