New Delhi, May 10 -- Alphabet Inc. shareholders have fretted over long-term risks posed by artificial intelligence to the company's money-printing search business for over an year. This week the threat became much more immediate. Alphabet shares ended the week down nearly 7%, while the Nasdaq 100 fell just 0.2%. The drop erased $138 billion in market value.

Court testimony from an Apple Inc. executive on Wednesday revealed that the iPhone maker is exploring adding AI services to its web browser for which Google now pays an estimated $20 billion a year to be the default search engine. Potentially more worrisome: searches on Apple's Safari fell for the first time last month, according to Eddy Cue, Apple's senior vice president of services....