Google's own AI answers just cost it $500 billion in a day

Alphabet shares fell about 12 percent on October 29, erasing almost $500 billion in market value — from $3.97 trillion to $3.46 trillion — in the company's worst trading day ever and, according to the Financial Times, the second-biggest one-day loss in Wall Street history.

The trigger was the third quarter: search advertising came in at $63.35 billion against roughly $64.85 billion expected, growth slowing from 19 percent earlier in the year to 12 percent, profit down 25 percent, and free cash flow negative $9.1 billion after more than $50 billion in AI spending. Google chief business officer Philipp Schindler told analysts that AI Mode queries bring lower monetization and eat into the money from ads beside traditional search results.

The irony is the story: Google's own answers are shrinking the ad business that pays for its AI buildout, and its reported fix is to put more ads inside AI Mode itself — selling inside the answers that took the clicks away.