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.
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.
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