New Bocconi University research using Comscore clickstream data found ChatGPT Search access reduced traditional search queries by 9.4% on average, deepening to 17% after twenty weeks. The substitution is real and it compounds.
The drop is not the headline. The trajectory is. Nine percent on arrival, seventeen percent by week twenty.
Researchers at Bocconi University have put a hard number on the question every SEO has been asked for two years. When people gained access to ChatGPT Search, their traditional search engine queries fell by 9.4% on average. After twenty weeks of exposure, the decline deepened to 17%.
The study, titled Answering Without Referring: How AI Search Rewrites the Web's Economic Bargain, draws on URL-level Comscore desktop clickstream records spanning October 2024 through July 2025. The window captures the staggered rollout of ChatGPT Search across OpenAI's user tiers, which gave the researchers a natural experiment rather than a survey.
That method matters. Most of the AI search debate runs on vibes and platform-reported numbers. This is observed behaviour from real clickstreams, and it shows substitution is not a one-off dip. It compounds as the habit forms.
The paper's title gives away the sharper finding. AI search answers without referring. Users get what they need and the website that supplied the information never sees the visit.
Why it matters
Australian businesses have spent two decades building acquisition strategies with organic search as the load-bearing wall. That wall is not collapsing, but it is thinning, and the rate of thinning accelerates with habit formation.
The commercial risk is concentrated in informational traffic. Queries that AI can answer in a paragraph are exactly the queries that used to deliver top-of-funnel visitors to content pages. Transactional and local intent is holding up far better, which changes where SEO effort should go.
The decline in traditional search queries after twenty weeks of ChatGPT Search access, according to Bocconi University's analysis of Comscore clickstream data.
What to do about it
Segment your organic traffic by intent before you panic. Split informational pages from commercial and local pages in your analytics. The risk profile of each bucket is completely different and averages will mislead you.
Baseline your AI referral traffic now. GA4 added an AI Assistant channel in May. Watch it monthly alongside organic, because the businesses that track the shift early will reallocate before their competitors notice it happening.
Stop producing content AI can fully answer. A 600-word definitional post is free training data with no return. Proprietary data, opinion, tools and local specificity are the formats that still earn the click.
Measure brand search as a health metric. If people ask an assistant for a recommendation and then search your name, that branded query is the new referral. Growing brand search volume is the strongest hedge against shrinking generic volume.
Price the shift into next year's plan. If informational organic delivers a meaningful share of your leads, model a 10 to 20% decline scenario and decide now which channels absorb the load.
The substitution is measurable, it compounds and the window to adjust calmly is still open.