Danny Sullivan of Google confirmed on Twitter that the search company launched the subtopics ranking feature or algorithm in mid-November 2020, just weeks after announcing it at the Search On event in October 2020.
Subtopics according to the announcement is a (machine learning) way for Google to "understand subtopics around an interest, which helps deliver a greater diversity of content when you search for something broad." "As an example, if you search for “home exercise equipment,” we can now understand relevant subtopics, such as budget equipment, premium picks, or small space ideas, and show a wider range of content for you on the search results page."
Danny Sullivan added on Twitter "subtopics don't change the look of search results, only broaden the diversity of content, when useful."
Here is the GIF Google uses to illustrate it, but it can't really be illustrated:
Here is Glenn Gabe asking Danny Sullivan about when it launched:
Mid-November 2020
— Danny Sullivan (@dannysullivan) January 9, 2021
Glenn asked Danny if what he was seeing with topic tags in Interesting Finds was related to subtopics announced in October:
This is a feature to help users find related Interesting Finds. It's not using the subtopics system. That is live now, but subtopics don't change the look of search results, only broaden the diversity of content, when useful.
— Danny Sullivan (@dannysullivan) January 8, 2021
Glenn tweeted some points as well:
BTW, nobody noticed the subtopics system was live. :) I thought I was seeing something related with Interesting Finds (and the topic tags being tested), but Danny explained that's not related to the subtopics system. Here's the post mentioning subtopics: https://t.co/XbQzgDo0J2
— Glenn Gabe (@glenngabe) January 9, 2021
Note, this is from the same announcement around Passage indexing which did not yet go live and also won't look different.
Did no one really notice? It depends. We reported on a few unconfirmed Google ranking updates; November 5th, November 11th, November 17th & 18th and November 25th.
Forum discussion at Twitter.