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LLM fabricates evidence by inventing quotes, developer finds

A developer building a causal-chain intelligence system discovered that the LLM used for evidence extraction was fabricating quotes from source documents. These fabricated quotes, often created by stitching together sentences from different parts of an article with ellipses, appeared highly credible but did not exist in the original text. The issue was exacerbated by truncating articles to fit context windows, leading the model to invent evidence when the actual supporting text was cut off. The developer implemented a fix by ensuring that extracted evidence quotes are exact substrings of the source documents, rejecting any relation if the quote is not literally present, and also cleaned up previously committed data containing fabricated evidence. AI

IMPACT Highlights the risk of LLMs fabricating evidence, necessitating deterministic checks over generative verification for critical applications.

RANK_REASON The cluster describes a specific technical problem encountered with an LLM and the developer's solution, akin to a research finding or a detailed technical report. [lever_c_demoted from research: ic=1 ai=1.0]

Read on dev.to — LLM tag →

AI-generated summary · Google Gemini · from 1 sources. How we write summaries →

COVERAGE [1]

  1. dev.to — LLM tag TIER_1 English(EN) · Tae Kim ·

    How I Caught My LLM Fabricating Its Own Evidence

    <p>The language model behind my Graph RAG pipeline did something worse than getting a fact wrong. It fabricated the evidence. Each relation it extracted carried a quote that was supposed to come straight from the source article, and many of those quotes had never been written. Th…