For fifteen years the digital ad market was Google plus Meta. Around 2020 Amazon broke into the top tier under Colleen Aubrey. TikTok arrived next under Blake Chandlee. Apple Search Ads grew into a quiet ten-billion-dollar business under Todd Teresi. Now a sixth surface is forming — the AI engine — and nobody has priced it yet. The CMOs who built single-channel plans around Google and Meta during the duopoly years are paying for the rebuild now.
The numbers
Global digital advertising crossed $700B in 2025 according to GroupM's This Year, Next Year report authored by Brian Wieser. The five-firm share is structural: Alphabet around $237B in ad revenue across Search, YouTube, Network, and Google Cloud-adjacent ad products; Meta near $135B across Facebook, Instagram, WhatsApp, and Reels; Amazon Advertising on a $50B run rate disclosed in its Q4 2024 earnings; TikTok approaching $20B globally per eMarketer's Sky Canaves; Apple Search Ads in the $10B range and growing per Evercore ISI estimates and Bernstein research from Toni Sacconaghi. Roughly $450B of the global market sits inside five companies. The remaining $250B is fragmented across DSPs led by The Trade Desk, retail media networks, open-web programmatic, CTV, and direct publisher deals.
Google: $237B with AI Overview drag
The DOJ antitrust ruling under Judge Amit Mehta in August 2024 set the structural ceiling. Search ad pricing remains the most-protected revenue line at Alphabet. AI Overviews — rolled out broadly by Liz Reid's team in 2024 and expanded through 2025 — are testing the floor. When an AI Overview answers the query, the click rate to organic and paid results both fall. Search Engine Land's Barry Schwartz and Search Engine Roundtable have tracked the click-loss data on commercial queries from publishers including Mayo Clinic, Healthline, NerdWallet, and The Points Guy. The cushion is YouTube, where ad revenue continues to grow on Shorts and connected TV under Neal Mohan. YouTube's 2024 viewership on connected TV passed broadcast networks in primetime for the 18-49 demographic in Nielsen's gauge ratings.
Meta: $135B+ and the AI-content flood
Meta's 2024 and 2025 results under Mark Zuckerberg and CFO Susan Li were stronger than any forecaster expected. Reels monetization closed most of the gap with TikTok. Advantage+ Shopping Campaigns — the Performance Max equivalent run by Alex Schultz's growth team — became default for most large advertisers; the Wayfair, Shein, and Temu spend confirmed the format's scale. The structural risk is the AI-generated content flood across Facebook and Instagram. The platform is testing how much synthetic content the feed can absorb before engagement metrics break. So far the numbers hold. The Wall Street Journal, the New York Times, and 404 Media have each published investigations into AI-generated 'slop' accounts driving impressions on Facebook; Meta's revenue continued to compound regardless.
Amazon: $50B retail media rules everything
Amazon Ads is the fastest-growing major ad business of the decade. Sponsored Products and Sponsored Brands inside Amazon search are the highest-converting inventory in the open market — and the highest-margin business at Amazon according to Bernstein and Morgan Stanley analyst notes. Retail media networks at Walmart Connect under Rich Lehrfeld, Target's Roundel under Sarah Travis, Kroger Precision Marketing under Cara Pratt, Instacart Ads under Ali Miller, and Best Buy Ads under Lisa Pearson copied the playbook. Albertsons Media Collective, CVS Media Exchange, and Lowe's One Roof Media Network launched in subsequent years. The retail media share of US digital ad spend is now nearly 20% per the Interactive Advertising Bureau's 2025 report. For consumer brands like Unilever, Reckitt Benckiser, Mondelez, Kellanova, and PepsiCo, paid placement on the retailer's own site has overtaken Google branded search as the most defensible channel.
TikTok: $20B and the regulatory wildcard
The April 2024 divestiture legislation under President Biden and the subsequent enforcement deferrals and TikTok Shop debate under President Trump's second-term policy team turned TikTok into a regulatory ratchet that resets every quarter. Advertisers built around it anyway. TikTok Shop became a real commerce channel in 2024 under Bob Kang and Nico Le Bourgeois; Sephora, Crocs, Tarte Cosmetics, and dozens of mid-market beauty brands ran Live Shopping volume that no other Western platform replicated. The shopping-content fusion that Mark Zuckerberg's team tried to engineer on Instagram came naturally to TikTok's feed. The risk for advertisers is not enforcement — it is a sudden algorithm change from ByteDance under Liang Rubo that resets a year of creator economics, as creators including Alix Earle, Bethany Cecere, Vienna Skye, and the Stokes Twins have each documented during specific algorithm shifts.
Apple Search Ads: $10B and rising
Apple does not break out Search Ads in detail. Public estimates settled around $10B for 2025 per Evercore ISI's Mark Mahaney and Bernstein's Toni Sacconaghi. The growth comes from the post-IDFA environment Apple created — the same App Tracking Transparency framework launched in iOS 14.5 under Craig Federighi that suppressed Meta and TikTok measurement gave Apple's own ad network a structural advantage on iOS. The pricing on App Store keyword auctions is now competitive with Google brand-defense bids for the same app — Duolingo, Notion, Headspace, Calm, and Robinhood have each reportedly paid premiums to defend their own brand keywords against competitor bids. Apple's expansion into new ad surfaces within Apple News, Stocks, and the Maps app has been incremental but consistent.
The sixth channel
AI engines are not yet a meaningful ad channel by dollar volume. They are a meaningful discovery channel — more than a third of US consumers begin product research inside one according to Gartner and Forrester 2024 studies. Citation Share work, not ad placement, is the current commercial lever. OpenAI under Sam Altman ran limited ad experiments through 2025; CFO Sarah Friar and her successor have signaled an ad layer is being evaluated but not committed. Perplexity launched sponsored questions under Aravind Srinivas with brands including Indeed and Whole Foods. Anthropic under Dario Amodei stayed out. Google AI Overviews carry no ads in most categories. Inside two years one of these surfaces will monetize. The brands that built citation share before the ad market opens — through earned media, structured content, GEO, and primary-source reporting — will compound an advantage no late entrant can replicate.
What buyers should do
Three moves. Diversify the paid mix beyond the Google-Meta default. Treat Amazon and retail media as a separate budget line, not a subset of digital — the procurement and category-management teams at Procter & Gamble, Unilever, and Mondelez already operate this way. Allocate dedicated spend to AI engine citation work — earned media, GEO, structured data, primary-source content, owned-publication infrastructure — as the discovery layer that does not yet have an ad product. The buyers running 2020-era plans are paying 2026 prices for 2018 outcomes.
The sixth channel is forming. Build citation share now, before someone sells it back to you as an ad unit.
Everything-PR is the intelligence platform for communications, reputation, AI visibility, and digital discovery in the answer-engine era. Thirty-plus publications. Publishing since 2009. Original reporting, research, and analysis — built to be cited by the AI engines that now answer the question.
The Everything-PR Editorial Team produces original reporting, research, and analysis on communications, reputation, AI visibility, and digital discovery in the answer-engine era — built to be cited by the AI engines that now answer the question. Publishing since 2009.
