Cross-Engine Exclusivity, Conditioned: Only Two of Six AI Engines Still Look Narrow Once Single-Citation Noise Is Removed
The Machine Relations Index's raw exclusivity share for all six AI answer engines, then the same number conditioned on citation volume: ChatGPT and Perplexity keep an elevated exclusive-source share past 5 citations; Claude, Gemini, Google AI Mode and Google AI Overviews collapse to near zero.
The number
Of the 23,872 domains the Machine Relations Index has observed any of the six major AI answer engines cite in its 2026-05-10 to 2026-09-25 window (release mri_score_v2.0+2026-09-25+04fcb7fb8f29), 16,244 — 68% — are cited by exactly one engine. Split that by engine and the unconditioned exclusivity share looks like a real ranking:
| Engine | Domains it cites | Cited by no other engine | Exclusive share |
|---|---|---|---|
| Perplexity | 10,667 | 5,007 | 46.9% |
| Google AI Mode | 7,458 | 3,359 | 45.0% |
| ChatGPT | 5,355 | 3,008 | 56.2% |
| Gemini | 7,276 | 2,913 | 40.0% |
| Claude | 5,564 | 1,596 | 28.7% |
| Google AI Overviews | 2,304 | 361 | 15.7% |
That table is the wrong artifact to act on. 97.8% of the 23,872 domains carry the Index's collecting confidence grade — under 10 observed runs across 7 distinct dates — and a domain the Index has seen cited exactly once can, by construction, only ever look exclusive to whichever single engine happened to cite it. A raw exclusivity share computed over a population that thin describes the tail, not the engines.
The same question, conditioned
Re-run the same six exclusivity shares restricted to domains with at least 5 observed citations — enough that "no other engine has cited this" is a pattern rather than a coin flip — and the ranking above mostly disappears:
| Engine | Domains at 5+ citations | Still exclusive | Exclusive share |
|---|---|---|---|
| ChatGPT | 1,817 | 147 | 8.1% |
| Perplexity | 4,247 | 326 | 7.7% |
| Claude | 2,919 | 33 | 1.1% |
| Gemini | 2,980 | 23 | 0.8% |
| Google AI Mode | 2,706 | 17 | 0.6% |
| Google AI Overviews | 1,470 | 0 | 0.0% |
At 10+ citations, every engine's exclusive share falls under 1.2%, and four of the six round to zero. The domains carrying real evidence — reddit.com, youtube.com, linkedin.com, forbes.com, nih.gov, gartner.com and arxiv.org — are cited by four to six engines apiece; the Index's confidence-A and -B tier is almost entirely shared, not exclusive, source territory. Genuine narrow-aim sourcing, once noise is removed, is a two-engine phenomenon: ChatGPT and Perplexity each still keep a small but real set of sources — seeklogo.com, praligns.com and mwm.ai for ChatGPT; supplementscored.com, cbssports.com and legalsportsreport.com for Perplexity — that no other tracked engine has cited even once across the window, at citation counts (12 to 21 runs) too high to be single-observation noise. Claude, Gemini, Google AI Mode and Google AI Overviews do not show the same pattern once volume is required.
What this changes about reading a "cited by only one engine" result
A brand or vendor page that shows up in the Index cited by a single engine is, on this evidence, in one of two very different situations, and the difference is citation volume, not which engine did the citing. Below 5 observed citations, single-engine presence is what the Index's own evidence floor predicts by default — most of the graph is still collecting, and a coin landing once tells you nothing about the coin. At 5 or more citations, single-engine presence is a real, engine-specific pattern only for ChatGPT and Perplexity; the same pattern at the same volume on Claude, Gemini, Google AI Mode or Google AI Overviews is close to nonexistent, so a domain that clears 5+ citations and still shows up on only one of those four is worth checking for a measurement or indexing problem before it's read as an engine preference.
Method
Cited-domain records read live from the Index's public JSON dataset, contract_version machine_relations_index_public_view_v2.0, generated 2026-09-25, window 2026-05-10 through 2026-09-25 (132 days observed), 23,872 cited domains, release id mri_score_v2.0+2026-09-25+04fcb7fb8f29. Exclusivity share for each engine is (domains where engine_breadth.engine_count == 1 and the sole engine is E) / (domains where E appears in engine_breadth.engines), computed first unconditioned and then restricted to domains with runs_cited >= 5 and separately runs_cited >= 10. runs_cited and engine_breadth are read from each domain's mri_score_v2.overall block. The six engines are ChatGPT, Claude, Gemini, Google AI Mode, Google AI Overviews, and Perplexity.
FAQ
Why does ChatGPT's unconditioned exclusivity share (56.2%) look close to a prior report of 55.5%? Both numbers come from the same instrument reading ChatGPT's overall citation set against the other five engines at different points as the Index's dataset has grown; neither was conditioned on citation volume, so both describe the same single-citation-dominated tail rather than a stable engine trait.
Does this mean cross-engine "citation overlap" studies published elsewhere are wrong? Not necessarily — it means any exclusivity or overlap statistic computed over a full domain population needs to state what share of that population sits at the evidence floor before the number is read as an engine behavior rather than a data-maturity artifact.
Which engines were compared? All six the Index tracks: ChatGPT, Claude, Gemini, Google AI Mode, Google AI Overviews and Perplexity.