Alphabet's Worst Trading Day Since 2004 and an Ad Tech ID Scandal

Alphabet shares fell roughly 13% on Thursday, the worst single day for the stock since the company went public in 2004, according to The Wall Street Journal. The trigger: slowing search ad revenue that management tied directly to its own AI product.

An investor on Wednesday's Q3 earnings call noted that Google's search revenue growth decelerated from 19% in Q1 to 17% in Q2 and 12% in Q3. Google's chief business officer, Philipp Schindler, confirmed that "the strong growth in AI Mode queries had an impact because of the lower monetization we were seeing in AI Mode."

What does the AI Mode disclosure mean?

Google's AI search business is not merely earning less per query than traditional search. It is actively dragging down total search revenue. "In a market worried about AI chatbots cannibalizing [Google's] key franchise, investors need to see [search] accelerating, not decelerating," David Wagner of Aptus Capital Advisors told the Financial Times.

Google's counterargument is patience. The company accepts short-term cannibalization of its strongest revenue line in exchange for growth later, once it loads AI search with ads.

Which ad tech vendors attached human IDs to bots?

A separate story broke this week in ad tech. An academic study co-authored by researchers at Indiana University and New Jersey Institute of Technology, working with Adalytics and DeepSee.io, documents misuse of extended identifiers (EIDs) — persistent user identifiers, such as hashed email addresses, used to track people across domains and devices.

The study found ad tech companies attaching real human tracking data to automated bots, making it appear that real people visited certain sites. Some vendors bundled multiple human IDs into a single bot session or advertising bid.

Per Jack Neff's writeup of the study:

• Zeta Global's LiveIntent was singled out for particularly brazen behavior
• Criteo, ID5 and Experian's Audigent assigned different EIDs to separate supply paths in multi-SSP auctions (auctions run across multiple supply-side platforms)
• Flashtalking was the only vendor of 18 studied never documented serving human EIDs to bots
• The Trade Desk came close to a clean record

The practice does not qualify as sophisticated invalid traffic under Media Rating Council standards. An MRC spokesperson said the organization "does not currently audit or accredit any identity solutions/providers nor audience targeting."

How bad was TelevisaUnivision's quarter?

Sports rights decided the quarter for TelevisaUnivision. US revenue fell 14% in Q3, with US advertising revenue down 24%, as rival Telemundo holds Spanish-language US rights to the 2026 FIFA World Cup.

Latin America offset the damage. TelevisaUnivision holds Latin American World Cup rights through its TV network and streaming service ViX. That coverage drove a 30% increase in subscription and licensing revenue overall; quarterly revenue in Mexico rose 51% and regional ad revenue grew 19%. Total company ad revenue declined 5%. Executives told investors they will keep expanding audience reach across linear and streaming, including a larger sports portfolio.

In brief

• WPP's Q3 revenue fell 2.1%, but WPP Media grew 0.3% — its first positive quarter in six, per Adweek. CEO Cindy Rose outlined shifted priorities since taking the helm last year.
• Health, food and news publishers saw the steepest organic search traffic declines over two years, with search ads as well as AI to blame, Search Engine Land reports.
• The Trump administration is increasingly subpoenaing Big Tech for information on users who criticize its immigration policies, per the WSJ.
• Nearly three months after acquiring CTV ad platform Vibe.co, Walmart let Vibe brand customers build campaigns with Walmart audience data, Adweek reports.
• Stagwell hired Alison Vacovec as SVP of growth for The Marketing Cloud.

The throughline for marketers: identity verification now sits outside accredited audit scope, and Google's AI transition has a measurable cost — a 12% Q3 growth rate that investors read as the start, not the end, of the adjustment.