Reddit’s share of citations in ChatGPT Search collapsed by 86.4% relative to its prior baseline over four days in mid-August, Search Engine Land reported, citing new tracking from AI-visibility firm Promptwatch. The firm says it cannot yet explain what caused the move. It is treating its own figures as provisional while it checks for a flaw in how the data was collected.

Promptwatch measured Reddit holding a 3.83% average citation share in ChatGPT Search from July 18 through Aug. 7, a stretch of relative stability. That average sank under 1% on Aug. 14 and settled at 0.52% for the Aug. 14 to Aug. 17 window. The gap between 3.83% and 0.52% is 3.31 percentage points. Expressed against the earlier baseline, that same gap is the 86.4% figure widely cited, a relative decline, not a percentage-point one.

A smaller, separate decline came first. On Aug. 8, Reddit’s ChatGPT Search share slipped out of the high-3% range and into the mid-2s, the same day Promptwatch logged a shift in how ChatGPT assembles its background fanout searches. The share of those fanout queries scoped with the site: operator jumped to 16.8%, up from 0.37% one day earlier, a roughly 46-fold increase. Promptwatch co-founder Klaas Foppen wrote in the firm’s report, cited by Search Engine Journal, that ChatGPT “is no longer just searching the open web and seeing what comes back; it is deliberately going to specific sites to pull information from them.” Fanout searches per ChatGPT reply also nearly doubled on average that day, moving from roughly 1.08 to 1.83.

That fanout shift does not explain the larger drop. Search Engine Journal reported that the site: operator’s share of fanout queries held roughly steady, in the 16% to 17% range, from Aug. 8 onward. Reddit’s citation share did not fall under 1% until six days later, on Aug. 14, with no matching change in fanout behavior recorded that day. A mechanism that stayed flat for a week is not a convincing explanation for a drop that arrived a week after it appeared.

Promptwatch did not find a similar single-day drop anywhere in Google’s AI products. Its Google AI Overviews citation share for Reddit drifted lower across the summer: about 2.5% at the start of July, near 2.1% by August. AI Mode’s Reddit citation share started easing near the end of July and kept sliding into August. Neither pattern resembles the sudden drop that Promptwatch says was unique to ChatGPT.

Search teams have watched this shape before. Several AI-visibility trackers flagged a comparable collapse in Reddit’s ChatGPT citation share back in September 2025, and coverage of it moved Reddit’s stock price at the time.

G2 growth advisor Kevin Indig later argued, in hedged terms, that the actual cause was not any decision by OpenAI or Reddit. He pointed instead to Google’s removal of the num=100 search parameter around Sept. 10, 2025, which had let SEO tools and data vendors pull up to 100 results per query. That change, Indig argued, made it harder for outside data providers, including ones OpenAI buys search results from, to reach the deeper results pages where Reddit threads often rank. He stopped short of calling it certain.

A citation share is a measurement of a system that neither Promptwatch nor the search team reading its report controls. When that measurement swings 86% in four days, the first question is not what Reddit did or what OpenAI changed. It is whether the platform moved or the measurement did, and Promptwatch cannot yet answer that for its own numbers.

Promptwatch has not closed the investigation. The firm is watching for a rebound in Reddit’s numbers and checking whether Aug. 14 reflects a genuine platform change or a flaw in how it collects data. Search teams should not wait for that answer. Pull your own domain’s ChatGPT and Google AI Overviews citation logs against the same dates, July 18 through Aug. 17, before making any Reddit-dependent GEO decision. An 86% swing in one vendor’s average says nothing about whether your own citations moved at all.

Reported by Search Engine Land (Danny Goodwin, Aug. 19, 2026), with additional analysis from Search Engine Journal.