Google is well-known for constantly experimenting with new designs and UI changes, mostly via limited server-side tests. What we see here is no different; the company seems to be trying out a more rounded search bar, one that matches more closely with the one seen on the Pixel Launcher, on its mobile site.
left: Old. right: New.
Along with the reshaping of the search bar, there are a couple of other changes.
Google is testing a rounded search bar on its mobile site was written by the awesome team at Android Police.