Reddit, Citation Instability, and the AI Purchase Recommendation Layer

Reddit accounts for 46.7% of Perplexity's top-cited sources on commercial and recommendation queries — the query category most directly linked to AI-driven purchase decisions. This concentration creates a structural vulnerability in brand AI positioning that is absent from conventional citation-based measurement frameworks. This paper documents the scale of Reddit dependency across major LLM platforms, examines the legal and operational volatility risks that can collapse this dependency rapidly and without warning, and proposes a measurement framework based on Conversational Survival Rate (CSR) and PSOS resilience scoring as the appropriate instrument for brands managing exposure to platform-dependent citation risk.