Citation drift

The largest public measurement re-sampled 82,619 prompts weekly for 17 weeks — December 17, 2025 to April 8, 2026 — producing 1,548,213 snapshots across six countries and three surfaces. It found Google replacing 56% of the sources in its AI answers every week and ChatGPT Search as much as 74%.

The structure matters more than the headline rate. For 86% of prompts there is a stable core of a few domains, with everything outside that core rotating at 89% per week. On Google AI Overviews specifically, 53% of prompts saw no source change at all across the full 17 weeks. Aggregate churn and per-prompt permanence are both real: they describe the rotating tail and the persistent core of the same answer.

Two consequences follow directly. AI Overviews and AI Mode cite different domains 83% of the time, so a citation-share figure measured on one Google surface is not a reading of the other. And only 1.4% of cited news articles stayed in the citation set permanently, which makes an AI citation behave, for a publisher, less like an asset that accrues than a placement that expires. Brands fare better: 43% of brand queries kept the brand's own domain present in all 17 weeks, while the co-citations beside it rotated at 70% per week.

Drift has more than one cause, and they are worth separating because only some are addressable. The engine's preferences can shift — AI Mode's publisher mentions fell nearly by half in thirty days while retailer mentions tripled across 15 of 20 verticals. Its retrieval method can change — Reddit's 86.4% four-day fall in ChatGPT citations traced to a change in how the engine assembles its background queries. And the model underneath can be swapped at any time, which the glossary's citation-share entry has flagged since it was written. None of those is something a page can be optimized against.

Measurement is arriving. Profound shipped a feature called Citation Decay in August 2026 that tracks week-over-week counts for every cited URL rather than reporting a point-in-time total — the longitudinal view this research argues is the only honest one.