Fifteen days ago, Reddit appeared in 87% of Perplexity's answers to our 39 buyer questions — the most inevitable source we had ever measured. We re-ran the identical questions through the identical pipeline. It's 18%.
39 identical questions · 15 days apart · same engines, prompts, gateway, extraction · source-level figures are Perplexity only
Only seven questions cited Reddit both times. And the two controls say this is Reddit-specific, not a citation drought: answers actually got richer (8.4 → 9.1 cited domains per answer), and YouTube barely moved.
| Set A — identical 39 questions | July 1 | July 16 |
|---|---|---|
| Answers citing Reddit | 34 / 39 = 87% | 7 / 39 = 18% |
| Reddit's share of all citations | 10.4% | 2.0% |
| Answers citing YouTube (control) | 15 / 39 = 38% | 14 / 39 = 36% |
| Cited domains per answer (control) | 8.4 | 9.1 |
The hole Reddit left was filled — largely by editorial and listicle publishers. Community corroboration was swapped for edited, publisher-shaped pages.
If that direction holds, the pool got more winnable by published pages — which is most of what a brand can actually control — and less dependent on being talked about in threads.
The single top-cited source changed on 31 of 39 questions (79%) in fifteen days. And at the brand level, each engine barely agrees with itself across the fortnight:
| Engine | Overlap with its own July 1 brand list |
|---|---|
| Perplexity | 25% |
| ChatGPT | 37% |
| Gemini | 38% |
| For scale: two different engines, same day | 7.5% |
"Your brand ranks on ChatGPT" is a statement with a half-life measured in days.
While the contents shuffled wholesale, the shape of the system did not move:
| Structural metric — Set A | July 1 | July 16 |
|---|---|---|
| All 3 engines shared ≥1 pick | 56% | 59% |
| At least 2 engines shared ≥1 pick | 90% | 87% |
| Full-list overlap (mean Jaccard) | 7.2% | 7.5% |
Every structural claim this series has published survived the fortnight. Every source-specific fact was perishable. That asymmetry is the strategy: optimize for the structure — be citable, be structured, be in the pool — not for any single incumbent source.
Founder, HarperFlow
A University of Cambridge graduate and medical doctor turned creator — his YouTube channel NeuroEverything has grown past 40,000 subscribers breaking down brain science. He later turned automation engineer, building content pipelines for founders and creators who'd rather build than market. He started HarperFlow on one conviction: great ideas deserve exposure, and the people best at building things usually have the least time to promote them. He writes from the workbench — HarperFlow runs its own pipeline, on its own blog, first.
In the full July 16 scan (250 questions), Reddit appears in 13% of answers and holds 1.8% of all citations — 36 thread URLs spread across 30 different subreddits, none appearing more than three times. The subreddit taxonomy we had planned is therefore moot: there is no concentration left to map.
"Reddit is 87% of AI answers" was true, measured — and lasted under fifteen days. Ask anyone quoting a citation stat when it was measured, and how often they re-measure.
The durable facts are structural: engines disagree, agreement is shallow, the pool is a long tail. Structured, citable pages on your own domain competed in both versions of this landscape; a Reddit-thread strategy competed in exactly one.
Monthly is now the minimum honest cadence. This series re-runs the same 39 questions every month and publishes whatever they say.
Its structural findings held; its Reddit reach figure did not — which is why it carries a dated update banner instead of a quiet edit.
| Metric | Scope | Value |
|---|---|---|
| Reddit presence — July 1 | Perplexity, Set A n=39 | 34 / 39 = 87% |
| Reddit presence — July 16 | Perplexity, Set A n=39 | 7 / 39 = 18% |
| Questions citing Reddit both runs | Perplexity, Set A | 7 |
| Reddit share of citations — July 1 | Perplexity, Set A | 10.4% |
| Reddit share of citations — July 16 | Perplexity, Set A | 2.0% |
| YouTube presence, July 1 → 16 | Perplexity, Set A | 38% → 36% |
| Cited domains per answer | Perplexity, Set A | 8.4 → 9.1 |
| Top-cited domain changed | Perplexity, Set A | 31 / 39 = 79% |
| Self-overlap over 15 days — Perplexity | brand lists, n=39 | 25% |
| Self-overlap — ChatGPT / Gemini | brand lists, n=39 | 37% / 38% |
| Cross-engine overlap, same day | all 3, July 16 | 7.5% |
| All-3 agreement, July 1 → 16 | all 3, Set A | 56% → 59% |
| ≥2 agreement, July 1 → 16 | all 3, Set A | 90% → 87% |
| Reddit presence, all 250 questions | Perplexity, July 16 | 33 / 250 = 13% |
| Reddit share of all citations | Perplexity, July 16 n=250 | 1.8% |
| Distinct subreddits / thread URLs | Perplexity, July 16 | 30 / 36 |
| Thread metadata fetches blocked | reddit.com, unauthenticated | 35 / 35 |
multi39.csv (July 1) and multi250.csv (July 16; Set A is the identical re-run) — and verify-numbers.py asserts every figure above straight from them. We don't know why the collapse happened — licensing, crawl access, retrieval re-ranking are all consistent with the data and none is verifiable from outside — so we report the measurement and decline to speculate.In 15 days, on byte-identical questions and an identical pipeline, Reddit fell from 87% of Perplexity’s answers to 18%, and the top-cited source changed on 31 of 39 questions (79%).
No. All-three-engine agreement went 56% → 59%, at-least-two went 90% → 87%, and full-list overlap went 7.2% → 7.5%. The rules held; the winners churned.
No engine agrees with its own two-week-old answers: brand-list overlap with July 1 was 25% for Perplexity, 37% for ChatGPT, 38% for Gemini.
Same method, pointed at your domain, re-measurable monthly. We'll ask the engines your buyers' questions and show you what they cite instead of you — with a date on it.
It's the same lesson we built HarperFlow around: in AI search, what you publish matters more than what you score — which is why we pitch it as a Surfer SEO alternative that publishes, not just grades.
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