Steven Levy, world famous author, wrote on Back Channel a bit about RankBrain, here is the quote:

It turned out the answer was yes, and the system is now part of search, known as RankBrain. It went online in April 2015. Google is characteristically fuzzy on exactly how it improves search (something to do with the long tail? Better interpretation of ambiguous requests?) but Dean says that RankBrain is “involved in every query,” and affects the actual rankings “probably not in every query but in a lot of queries.” What’s more, it’s hugely effective. Of the hundreds of “signals” Google search uses when it calculates its rankings (a signal might be the user’s geographical location, or whether the headline on a page matches the text in the query), RankBrain is now rated as the third most useful.

So back when they first announced it, it was used in about 15% of queries and now it is used in “every query.” And the impact is felt in “a lot of queries” but not every one he reported Google saying.

Danny Sullivan broke this out into a story last week and then updated his useful FAQ on RankBrain.

The weird part, I still don’t see how RankBrain is a ranking signal over a query interpreter or modifier.

We reported last week that RankBrain can’t be optimized for and there is no RankBrain score.

In any event, it is just confusing how Google has positioned RankBrain as a ranking signal in my opinion. Other than that, RankBrain is heavily used in search, whatever that means.

Search Engine Roundtable Forum discussion at Twitter.