Brainlabs Tracks 10.5% Fewer Sessions as AI Referrals Rise 163% Across 54 Clients

A 14-month look at Brainlabs’ 54 clients finds search sessions declining as AI-platform referrals and tracked visitor actions increase. For marketing teams, the immediate challenge is measuring a smaller but more active referral stream when some AI-originated visits may be classified as direct traffic.

Brainlabs analyzed Google Analytics data from 54 clients in 19 sectors between January 2025 and April 2026. The roster included 24 U.S. firms, 24 British brands and six clients in other markets; 29 employed at least 1,000 people. It is a view of one agency’s clients, not the advertiser market as a whole.

The September inflection point

Brainlabs identifies September 2025 as a turning point, when AI Overviews appeared on at least 30% of U.S. search-results pages. Average monthly organic sessions in its dataset then moved from about 20 million to fewer than 15 million. The timing shows a change in the client set, not proof that Overviews caused the decline.

The referrals that arrive do more

AI-driven key events rose 335% during the period. Brainlabs counts purchases, newsletter signups and scrolling to the bottom of a page among those events, so the measure captures advertiser-relevant activity rather than sales alone. Referrals from ChatGPT, Copilot, Gemini and Perplexity generated key events at 1.5 times the rate of organic-search visitors.

Commercial queries are the next test

The results varied by category. Fitness, fintech, insurance and consumer-packaged-goods clients saw some of the largest traffic declines, while retail, beauty and entertainment had some of the smallest. Brainlabs says Overviews have appeared mostly on educational and discovery queries, though they are beginning to extend to transactional and commercial searches; it also attributes retail’s relative resilience to fewer Overview triggers on transactional searches.

ChatGPT supplied the largest share of AI-search referrals before and after September 2025. But Brainlabs says referrals can be understated when a user opens a destination site in another browser window and the visit is logged as direct traffic. Its recommendation is to track AI search in routine KPIs alongside referrals, traffic and conversion events when planning paid media.