Reddit is the community domain with a real share. Quora's weight is a Google AI Overviews and AI Mode finding, and it does not transfer to Perplexity. Stack Exchange is absent from the published Perplexity leaderboards, which is not the same as a measured zero. "Social" is a bucket vendors define differently, and it is a poor synonym for forums.
- Perplexity is the engine where Reddit is a large fraction. 6.6% of all citations through June 2025, 24% on commercial prompts in January 2026, 21.6% of the US top-50 pool in September 2026.
- ChatGPT's comparable all-citation share was 1.8% in that same Profound window. Tinuiti's commercial panel had Reddit above 5% of ChatGPT citations in January 2026, and at 0.1% on Gemini.
- Quora is 4.7% of the AI Overview top-source pool and 3.0% of AI Mode's, in Ahrefs' September 2026 US lists. It is not in Perplexity's top 50 that month.
- Copilot ranked Reddit 31st in Profound's November 2025 cross-engine list, and Reddit is outside Copilot's September 2026 top 50.
- Profound's "social" bucket includes LinkedIn, Quora, Stack Overflow, G2, TripAdvisor, Medium, and Substack, and the include-list does not name YouTube. Tinuiti's social bucket includes YouTube. Do not compare 19% and 31% as one class.
Reddit, by engine
The cleanest like-for-like is Profound's share of all citations, August 2024 to June 2025. One dataset, three engines, one denominator.
| Engine | Reddit's share of all citations | Reddit's rank note |
|---|---|---|
| Perplexity | 6.6% | First. 46.7% of the top 10 only. |
| Google AI Overviews | 2.2% | First in that engine's top 10, at 21.0% of the ten. |
| ChatGPT | 1.8% | Second, behind Wikipedia. 11.3% of the top 10. |
Later ranks, from Profound's collaboration with Reddit, data through late October 2025: Perplexity 1, ChatGPT 2, AI Overviews 2, AI Mode 3, Grok 2, Copilot 31. The September drop they describe, from about 7% to about 1% and back to about 3%, is ChatGPT, not Perplexity. The post is vendor-aligned because Reddit commissioned it. The rank table is still the cross-engine list from that dataset.
Commercial prompts pull Reddit up. Tinuiti, January 2026: Perplexity 24% of all citations, ChatGPT above 5%, Gemini 0.1%. YouTube on those three was 3%, nearly none, and 0.7%. Evertune saw Reddit in 20% or more of Perplexity responses on some weeks in January and February 2026, among only four domains they tracked. Answer presence, not link share.
The September 2026 Ahrefs mention shares are a fourth reading and they are not comparable to the 6.6%. Perplexity: Reddit 21.6% of the top-50 pool. AI Overviews: 18.5%. AI Mode: 17.9%. ChatGPT: 16.8%. Gemini app: 28.5%. Copilot: not in the top 50. The engine order is the finding. The percentages are shares of a head, and they will all look large.
Quora is a Google finding
Profound's Overview top 10 through June 2025 has Quora third, at 1.5% of all citations and 14.3% of the top 10, behind Reddit and YouTube. Quora is not in the Perplexity top 10 of the same study. Across all models in the later Reddit collaboration, Quora was 0.39% of citations, tenth, and that figure is not split by engine.
Ahrefs, September 2026, US mention share: Quora is sixth on AI Overviews at 4.7% and seventh on AI Mode at 3.0%. A secondary report of a Semrush study says Quora was cited in 7.25% of AI Mode responses. That page was not re-fetched, so 7.25% stays a reported AI Mode figure and is not a Perplexity number. Carrying Quora's Google weight onto Perplexity is the recurring mistake in community roundups.
Forums, Stack Exchange, and the word social
Indexly's buyer-intent Perplexity panel, May to July 2026, prompt count undisclosed, puts community and forums at 18% of citations, with Reddit the leading domain at 8.2% of all citations. The authors say Quora and Stack Overflow follow inside the bucket, and they do not give shares. If every Reddit citation sits in that 18%, other forums are on the order of ten points combined. Indexly does not say the bucket is exhaustive of reddit.com, so the remainder is an inference, not a published Quora share. Partial
Profound's January 2026 social definition is wider: platforms where users publish freely, including Reddit, LinkedIn, Quora, Stack Overflow, G2, TripAdvisor, Medium, and Substack. Perplexity's social share in that table is 19%, prose 19.4%. ChatGPT is 5%. AI Overviews and AI Mode are 7%. Claude and Copilot are 3%. The opening sample sentence names three engines and the table has seven. No date range is given. This 19% is not a forums share.
Japan is the reminder that "community" is not a synonym for Reddit. An October 2025 Ahrefs count had Yahoo! Chiebukuro first on Perplexity there, and it had left the top five by March 2026. A local Q&A site can be the whole category, and then it can leave.
What this does not prove
Open question It does not say what gets cited when no Reddit thread exists. That counterfactual has not been measured. The unconditional runners-up, and the pre-registered study, are linked from the Reddit dependency page. It also does not say a brand should open a forum. The advantage in these tables is an archive that already exists at Reddit's scale, not the format in the abstract.
How to use the list
Match the engine. A Perplexity plan that ignores Reddit is ignoring the measured leader. A Copilot plan that starts with Reddit is ignoring a 31st-place rank and a top 50 that does not contain it. A Quora plan is a Google plan. Stack Exchange is a hypothesis until someone publishes a share.
The August 2026 break in ChatGPT's Reddit share is a time-series question, not a community-mix question. It is on how the list changes.
Quora's citation weight is a Google finding. On Perplexity it is not in the published top 50. Reddit is the community domain the studies actually count.
Share on XVerification status
Reddit shares are labelled with their denominator. Quora's Perplexity share was not invented to fill a cell. Stack Exchange is reported as absent from named lists. A Semrush "40.1% of AI answers cite Reddit" figure could not be traced to an original URL and is not used.
Namdev, R. (2026). Most-cited community domains in AI search (v1). Retrieved from https://ritiknamdev.com/blog/most-cited-community-domains-ai-search Published under CC BY 4.0 — reuse freely with attribution.
Perplexity's domain list is most-cited domains in Perplexity. The gap study is what Perplexity cites when Reddit is silent.