It appears that Google is testing more tweaks to their In-Depth Articles section in the Google Search results.  They appear to be testing a variation of it with the thumbnail images removed.

Here is how they are currently appearing for US users.

Google has been showing thumbnails for in-depth articles:

This is the second tweak Google has made to the in-depth articles section of the search results in recent weeks.  They were previously testing it with and without the “In-depth articles” header on top of the section of results, which appears to be default now for all users.

It doesn’t appear that Google has made any additional changes to the number of search results Google is displaying the in-depth articles on, as Mozcast data shows it holding steady at 12% of the queries they track.

This change of removing the thumbnails definitely makes those articles not as noticeable as they were.  And with the in-depth article header removed, they are definitely well blended into the search results so that the majority of users wouldn’t realize that that particular set of results was a higher level and more in-depth than the rest of the search results on the page.