Mainly: What happens to the company if lots of people start using AI engines to answer questions instead of Google's dominant search engine? Now it looks like that might actually be happening. Apple executive Eddy Cue says searches on Apple's Safari browser shrank for the first time ever in April — a change he chalked up to people using AI instead.

While the full impact of Apple’s potential move into AI search is yet to be seen, Alphabet’s stock reaction reflects immediate investor concern over the company’s ability to maintain its search-related revenue if Apple becomes a competitor in this space. Shares of Apple also declined, falling 2%.