Google's CEO, Sundar Pichai, testified before congress not too long ago (as you may remember) and one thing that he said that stood out to me was that Google has over a thousand people working on core search. It wasn't clear if those were just engineers or it also included contractors, designers, Doodlers, etc.
But he did specifically say "core search." At around 3 hours and 6 minutes into the testimony, a congressman asked Sundar Pichai how many staffers do they have working on search at Google. Sundar said "Congressman, today it is our search team, which works on core of our search team, and there is well over a thousand people."
Here is the video embed that starts at the time he said it:
I suspect this is just people on core search, but not just core ranking. Things like search quality, search ranking, snippets, indexing, crawling, etc etc. I do not know if he was including those who work on user interface design or not.
But when Google says core search, my head goes to core search algorithm updates.
It was a brief question with a brief answer.
Forum discussion at YouTube.