ObsurfableSeptember's Brand Radar refresh is the first month where Perplexity's #1 source is Reddit, not YouTube. Google's own properties keep climbing on AI Mode and AI Overviews. ChatGPT's top 10 still starts with Reddit and Wikipedia — but the middle of the table rotated toward Consumer Reports, NIH/PubMed, and .gov health domains while August's dictionary surge partially unwound.
This report updates our August 2026 leaderboard with Ahrefs Brand Radar monthly snapshots dated September 2, 2026 (US, all topics). Mention share = each domain's citations as a percentage of the summed citations of the top 50 sources on that assistant. Figures are directional within each platform's methodology — not directly comparable to live-interface citation trackers like Promptwatch, which logged a separate ChatGPT Reddit cliff in mid-August.
Consensus leaderboard: same giants, sharper splits
Reddit, YouTube, and Wikipedia still anchor the cross-engine map. What changed in September is who leads where, not whether the mega-domains matter:
| Rank | Domain | Role in AI answers |
|---|---|---|
| 1 | Community consensus — now #1 on Perplexity as well as ChatGPT and AI Mode | |
| 2 | YouTube | Video evidence — still #1 on AI Overviews; close #2 on Perplexity and AI Mode |
| 3 | Wikipedia | Entity and definitional anchor — softer on ChatGPT this month (7.0%) |
| 4 | google.com | Self-citation via profiles and panels — 12.5% in AI Mode, 8.8% in AI Overviews |
| 5 | Facebook / Instagram / Quora | Google-surface social layer |
| 6 | Forbes / NYT / Business Insider | Editorial — climbing on Perplexity (NYT ▲ 28) |
| 7 | NIH / PubMed / FDA / CDC | Institutional health — multiple ChatGPT climbers |
| 8 | Amazon / Walmart / Target | Commerce and retail evidence |
SurfacedBy's 2.7% all-five-engine domain overlap and Foglift Q3's 0.094 mean pairwise Jaccard still describe the structure underneath: concentration at the top, almost no shared leadership across engines.
Hard numbers by platform (Ahrefs Brand Radar, September 2026)
ChatGPT
| Rank | Domain | Mention share | MoM signal |
|---|---|---|---|
| 1 | reddit.com | 16.8% | Stable |
| 2 | en.wikipedia.org | 7.0% | ▼ |
| 3 | consumerreports.org | 3.7% | ▲ 1 |
| 4 | forbes.com | 3.1% | ▲ 1 |
| 5 | engineerfix.com | 2.8% | ▲ 3 |
| 6 | legalclarity.org | 2.8% | ▲ 1 |
| 7 | healthline.com | 2.5% | ▲ 2 |
| 8 | youtube.com | 2.5% | ▲ 7 |
| 9 | pmc.ncbi.nlm.nih.gov | 2.4% | ▲ 8 |
| 10 | walmart.com | 2.3% | ▲ 1 |
What changed: August's reference inflation partially reversed — Merriam-Webster fell 9 places, Cambridge Dictionary 13, Dictionary.com 24, Collins 33. In their place: Consumer Reports at #3, NIH/PubMed in the top 10, and FDA and CDC entering the top 50 as NEW. YouTube ticked up to 2.5% (▲ 7) but remains a minor ChatGPT source. Trustpilot (▲ 14) and BBB (▲ 15) signal review/trust infrastructure rising.
Methodology note: Promptwatch reported ChatGPT Search's Reddit citation share collapsing to ~0.5% in mid-August. Ahrefs Brand Radar still shows reddit.com at 16.8% mention share in September's broad US query panel. Those numbers measure different things — live citation share among cited answers vs. domain weight in the top-50 source stack. Do not assume one invalidates the other; track both if ChatGPT is primary.
Perplexity
| Rank | Domain | Mention share | MoM signal |
|---|---|---|---|
| 1 | reddit.com | 21.6% | ▲ 1 |
| 2 | youtube.com | 20.8% | ▼ 1 |
| 3 | en.wikipedia.org | 6.3% | Stable |
| 4 | facebook.com | 4.5% | Stable |
| 5 | amazon.com | 3.6% | ▲ 1 |
| 6 | healthline.com | 2.6% | ▲ 3 |
| 7 | alibaba.com | 2.0% | ▼ 2 |
| 8 | oreateai.com | 1.8% | ▲ 4 |
| 9 | goodhousekeeping.com | 1.7% | ▲ 11 |
| 10 | nytimes.com | 1.6% | ▲ 28 |
What changed: The month's headline — Reddit overtook YouTube for the #1 slot. YouTube fell from 31.2% to 20.8% mention share while Reddit rose to 21.6%. The two are now nearly tied; Perplexity is no longer a YouTube-first engine in Brand Radar's top-source accounting. Health editorial climbed (Healthline, WebMD, NIH NEW, Cleveland Clinic NEW). NYT jumped 28 places into the top 10. TikTok Shop fell 35 places — social-commerce retrieval cooled. Automotive domains (Edmunds ▼ 14, KBB ▼ 17, Cars.com ▼ 23) rotated down as health and editorial rose.
Google AI Overviews
| Rank | Domain | Mention share | MoM signal |
|---|---|---|---|
| 1 | youtube.com | 22.9% | ▲ |
| 2 | reddit.com | 18.5% | Stable |
| 3 | facebook.com | 10.1% | ▼ |
| 4 | google.com | 8.8% | ▲ |
| 5 | instagram.com | 5.6% | Stable |
| 6 | quora.com | 4.7% | Stable |
| 7 | en.wikipedia.org | 4.0% | Stable |
| 8 | tiktok.com | 3.3% | ▲ 1 |
| 9 | amazon.com | 3.3% | ▼ 1 |
| 10 | walmart.com | 1.0% | Stable |
What changed: YouTube ticked up to 22.9% (from 21.1% in August). google.com rose to 8.8% (from 7.1%) — the self-citation shift continues on Google's largest AI surface. Forbes, Healthline, NYT, and Trustpilot climbed in the long tail. Editorial domains (CNBC, Byrdie, RTings NEW) entered or rose — a slight tilt toward review and explainer publishers beneath the UGC layer.
Google AI Mode
| Rank | Domain | Mention share | MoM signal |
|---|---|---|---|
| 1 | reddit.com | 17.9% | ▼ |
| 2 | youtube.com | 17.8% | ▲ |
| 3 | google.com | 12.5% | ▲ |
| 4 | facebook.com | 10.2% | ▲ |
| 5 | instagram.com | 5.7% | Stable |
| 6 | en.wikipedia.org | 4.0% | Stable |
| 7 | quora.com | 3.0% | ▲ |
| 8 | amazon.com | 3.0% | Stable |
| 9 | tiktok.com | 2.7% | Stable |
| 10 | walmart.com | 1.5% | Stable |
What changed: Reddit still leads but share eased (19.9% → 17.9%). YouTube nearly tied at 17.8%. google.com hit 12.5% (from 11.5%) — now a clear #3 and the fastest-rising structural source on AI Mode. Forbes (▲ 3), NYT (▲ 10), and LinkedIn (▲ 3) moved up. AI Mode and AI Overviews still behave as separate scoreboards (~11–14% URL overlap on matched prompts in prior Ahrefs panels).
Side-by-side: same domain, different engines
| Domain | ChatGPT | AI Mode | AI Overviews | Perplexity |
|---|---|---|---|---|
| 16.8% | 17.9% | 18.5% | 21.6% | |
| YouTube | 2.5% | 17.8% | 22.9% | 20.8% |
| Wikipedia | 7.0% | 4.0% | 4.0% | 6.3% |
| google.com | — | 12.5% | 8.8% | — |
| 1.4% | 10.2% | 10.1% | 4.5% | |
| Forbes | 3.1% | 1.0% | 0.8% | 1.2% |
| Consumer Reports | 3.7% | 0.5% | 0.4% | 1.3% |
YouTube is still ~9× more important on AI Overviews than on ChatGPT by mention share. Reddit now leads on all four assistants in this snapshot. google.com matters only on Google surfaces — and keeps rising. Forbes and Consumer Reports matter far more on ChatGPT than on Google AI Overviews.
Claude: still the editorial outlier
Claude's citation personality did not change this month. It still barely cites Reddit or YouTube in controlled samples, favoring prestige editorial, documentation, and institutional sources instead. If your program is Claude-heavy, September's Perplexity Reddit flip and ChatGPT dictionary unwind are noise — your path remains earned coverage in high-trust publishers and verifiable primary data.
Month-over-month themes worth watching
1. Perplexity's YouTube → Reddit handoff. First Brand Radar month with Reddit #1 on Perplexity. Video is still #2 at 20.8%, but the "YouTube owns Perplexity" story from July–August is over — for now.
2. google.com keeps rising. 12.5% in AI Mode and 8.8% in AI Overviews. Business Profile completeness, product feeds, and entity consistency are citation infrastructure.
3. Health and institutional sources on ChatGPT. NIH, PubMed, FDA, CDC, Mayo, Cleveland Clinic — multiple climbers as dictionary sites fell back. YMYL queries may be pulling toward primary medical sources.
4. Dictionary unwind on ChatGPT. August's Merriam-Webster / Cambridge surge was not durable. Reference sites can spike and fade within weeks.
5. Two ChatGPT Reddit stories. Brand Radar: stable ~16.8%. Promptwatch mid-August: citation-share cliff. Measure the metric your buyers actually hit.
6. Volatility remains structural. Ahrefs still notes ~70% chance an AI Overview changes between observations. Monthly Brand Radar refreshes are the floor, not the ceiling, for monitoring cadence.
The long tail is still where most brands win
The giants dominate the leaderboard. They do not own every citation. SurfacedBy: 69.6% of domains cited by exactly one engine. Geonimo: 73.5% of citations outside the top 100 domains. Foglift Q3: 75% of combined top-25 domains exclusive to one engine.
You do not need to outrank Reddit. You need to be the clearest trusted page for the narrow prompts your buyers ask — and to show up on the engine they actually use.
What to do with the September map
- Re-check Perplexity strategy. Reddit and YouTube are now co-leaders. Community and video both matter; neither alone is sufficient.
- Audit Google-hosted surfaces. google.com at 12.5% on AI Mode is a product-visibility line item, not local SEO trivia.
- For ChatGPT YMYL: prioritize institutional health sources and trusted review orgs (Consumer Reports, BBB, Trustpilot) over dictionary SEO.
- Do not assume August's ChatGPT Reddit cliff killed Reddit everywhere. Google surfaces and Brand Radar's ChatGPT panel still show strong Reddit weight — engine-separated dashboards only.
- Measure weekly on a fixed prompt set. Monthly leaderboards lag policy changes that land mid-month.
Obsurfable runs that fixed prompt library across engines — mention, citation, and competitor columns separate — so you see Perplexity's Reddit flip and google.com's rise on your category prompts, not only in aggregate industry tables.
Bottom line
As of September 2026, Reddit leads all four major assistants in Brand Radar's latest snapshots — including Perplexity, where it passed YouTube for the first time. google.com is now a top-three AI Mode source at 12.5%. ChatGPT rotated from dictionaries toward health, reviews, and .gov. YouTube still owns AI Overviews (22.9%) while barely registering on ChatGPT (2.5%). The winning move is unchanged: engine-specific presence, long-tail specificity, and continuous measurement — because this leaderboard just proved again that it moves every month.
Primary figures from Ahrefs Brand Radar monthly most-cited tables (US, all topics; snapshots updated September 2, 2026). Corroborated with SurfacedBy, Foglift Q3 2026, Promptwatch August ChatGPT Reddit analysis, and related mid-2026 studies. Methodologies differ — treat percentages as directional within each platform's mention-share definition.