If you're one of those who has yet to even see the two-tab interface, you'll be surprised to hear that Google is already testing out a third tab. Reports indicate that the new button performs a search. The tab might be a bit redundant, given the search bar already present at the top of the page, but perhaps scrolling to the top was a bit too inconvenient for some.
We've received a few tips and comments about the new icon over the last week, and though it appears to be a widespread test, there isn't any pattern that we've noticed. Given the way the dual-tab setup before seems to work, you might not see it in the Google app if you have a Now-integrated launcher. Some users have reported that the tabs appear in their Google app outside a launcher, while others (such as myself) aren't able to see any of the new features via either method.
It's not a huge change since it's just bringing the same search feature already present down into its own tab, but it's interesting to follow the way they have been testing changes to the Google app UI, and the general proliferation of iOS-alike tabs in Google's apps. Hopefully, those of us with Pixel devices or incompatible launchers will be able to make use of the interface changes soon.
It looks like Google was also testing another tab as well, this time a "Recent" history tab.
- and Teemu