I analyzed 5.3M AI citations across 5 engines. ChatGPT cites Reddit more than any other website (we already knew this).
Quick disclosure up front: I work on an AI-visibility tracker (Vercite), and this is our data. Link's at the bottom – free to read. Posting here because the findings are genuinely useful for anyone working with AI visibility.
We looked at 5.31 million citations – every source link returned across ChatGPT, Perplexity, Gemini, Google AI Overview, and Google AI Mode – and classified 158,847 domains to see who each engine actually pulls from.
The headline for this sub: ChatGPT's single most-cited website is reddit.com. Not Wikipedia, not a news outlet. Reddit (most of us already know that).
But the bigger pattern is that each engine has a different "home platform":
- ChatGPT → Reddit
- Perplexity → YouTube
- Google AI Mode → YouTube (its #1 source overall)
- Google AI Overview → leans on both Reddit and YouTube
- Gemini → barely any of them (1.4% combined)
A few other things that stood out:
- The 5 engines agree on almost nothing. Pooling each engine's top-100 sources gives 253 distinct domains, and only 23 (9%) are cited by all five. More than half are cited by just one engine and no other. There is no single "AI-friendly" source list.
- Concentration varies wildly. Google AI Mode pulls half its citations from just 71 domains – a tiny club. ChatGPT spreads the same half across 712. AI Mode is winner-takes-all; ChatGPT rewards a long tail.
- Google's AI mostly cites Google. When AI Overview cites a google.com page, 79% of the time it's pointing back to its own Search results. 8.5% of everything it cites is a Google property.
Methodology / caveats (being upfront):
- Real citations from tracked prompts across all five engines, not a one-off lab test.
- We classified all 158,847 domains by source type (forum, news, official, brand-owned, etc.) rather than by industry, so the patterns reflect how each engine sources, not what any one set of prompts was about.
For those tracking AI visibility across engines: are you seeing the same Reddit/YouTube split, and are you optimizing per-engine or still treating "AI" as one channel?
Full write-up with all the charts: https://vercite.io/research/citation-landscape