Google has resumed the AdSense related search Custom search style experiments after pausing it back 8-months ago in May 2021. Google said “we’d like to inform you that as of January 6, 2022, we’ve re-enabled your ability to create Related search Custom search style experiments in your AdSense account.”
The pause originally was suppose to be for a couple of months, from May through July 2021. But I guess it carried on longer. Google wrote then “beginning May 10, 2021, you will not be able to create new experiments for your Related search styles in your AdSense account. Your existing Related search experiments that are currently in progress will also stop on May 10, 2021. Please note that this change does not prevent you from creating experiments for other elements of your styles (e.g., search ads, shopping ads).”
You can access this by clicking into Optimization and then Experiments and try to make a Custom search style, you may run into an issue soon.
Forum discussion at Twitter.
