Half the domains AI engines cite were gone six days later — unless more than one engine cited them.

Method, stated before the numbers

Both runs are production runs of the same instrument: 12 pinned buyer questions × 4 engines × 3 samples = 144 answers per run, citations read from each engine's returned citation array (not a substring test on prose), URLs collapsed to registrable domains, one count per (domain, answer). Run one (2026-07-28) cited 538 distinct domains; run two (2026-08-03) cited 506. A domain "survived" if any engine cited it anywhere in run two. Nothing about the questions, engines, sampling, or extraction changed between runs — the only variable is six days of engine behaviour.

Survival by how many engines cited you

The overall number — half the citation layer replaced in under a week, with 229 domains entering that were cited nowhere in run one — is the one that should reframe how a business reads any single AI-visibility report. But the split is the finding: the single-engine tail, which is 81.6% of everything the engines cite, churns at nearly 6 in 10, while the multi-engine core barely moves. Depth predicts durability the same way: domains cited on one answer survived at 28.3%, on 2–4 answers at 70.8%, on 5+ answers at 94.6%.

Engines differ in how much they forget

ChatGPT and Gemini kept fewer than half of their own citation sets across six days; Perplexity kept 71.1% of its. If your AI-visibility evidence is "ChatGPT cited this source last week," the base rate says that observation has roughly a coin-flip's chance of still being true this week — which is worth knowing before anyone builds a strategy, or sells one, on a single reading.

Limits

• Sampling and churn are entangled at the thin end. Each run samples each engine 3 times per question, so a domain cited once in run one can miss run two by sampling luck rather than any change in the engine. That is precisely the operational point — a domain seen once in 144 answers has no stable claim on the answer surface — but it means the 42.1% tail survival mixes "dropped" with "was never reliably there." The multi-engine rates, measured on domains too widely cited for sampling luck, are the clean signal.
• Two runs, six days. This is a first repetition, not a tracked series; retention could look different over a month. The instrument runs weekly, so the series now exists going forward.
• One question panel. 12 buyer questions about AI visibility for small businesses; other topics may churn differently.
• We have a commercial interest. We sell AI-visibility audits. Every number above is reproducible from the two dated citation cuts, which we share with anyone who asks.

The practical reading for a business: a screenshot of one AI answer naming you is weather, not climate. What persists is being cited by more than one engine, on more than one answer — the 99-domain core that survived at 90–100%. To see which engines currently cite anything about your business — and whether it is core or tail — run the measurement on your business in 60 seconds.