Google seems to have rolled out the refine this search filter button that overlays a number of search filters. This seems to be the mobile version of what we saw on desktop and honestly may have been out for some time but I never covered what it looked like (or maybe I did and I am getting old).
Valentin Pletzer posted some screenshots of this on Bluesky but I can also replicate this on my device. Here are his screenshots, notice the top left has this filter icon, next to the "Get it fast" search filter:
Then when you click on that filter, it overlays all these search filters:
Again, I can replicate this, so it makes me think this is no longer a test but fully live for those in the US and probably other countries.
Forum discussion at Bluesky.
