What they did
Semrush tracked the top 25 most-cited domains each week across ChatGPT, Google AI Mode and Perplexity for 13 weeks, from mid-July to mid-October 2025.
What they found
On ChatGPT, Reddit was cited in close to 60% of responses in early August, then fell to around 10% by mid-September; Wikipedia dropped from roughly 55% to under 20% over the same window. Google AI Mode was steadier, with LinkedIn in nearly 15% of responses and Wikipedia in about 2%. Perplexity leaned on Reddit, LinkedIn and NIH.
How much weight to give it
Over 100 million citations and 230,000 prompts make this one of the larger citation-source studies, and the weekly cadence caught a real platform shift rather than a single snapshot.
What it doesn't prove
One vendor, and the 13-week window happened to straddle a big mid-September change in ChatGPT's sourcing, so the domain shares are unstable. Gemini and Claude were not included and the prompt mix is not disclosed.