D-REX: A Benchmark for Detecting Deceptive Reasoning in Large Language
  Models
Authors: name: Satyapriya Krishna; name: Andy Zou; name: Rahul Gupta; name: Eliot Krzysztof Jones; name: Nick Winter; name: Dan Hendrycks; name: J. Zico Kolter; name: Matt Fredrikson; name: Spyros Matsoukas
Published: 2025-09-22 15:59:40

Abstract: The safety and alignment of Large Language Models (LLMs) are critical for
their responsible deployment. Current evaluation methods predominantly focus on
identifying and preventing overtly harmful outputs. However, they often fail to
address a more insidious failure mode: models that produce benign-appearing
outputs while operating on malicious or deceptive internal reasoning. This
vulnerability, often triggered by sophisticated system prompt injections,
allows models to bypass conventional safety filters, posing a significant,
underexplored risk. To address this gap, we introduce the Deceptive Reasoning
Exposure Suite (D-REX), a novel dataset designed to evaluate the discrepancy
between a model's internal reasoning process and its final output. D-REX was
constructed through a competitive red-teaming exercise where participants
crafted adversarial system prompts to induce such deceptive behaviors. Each
sample in D-REX contains the adversarial system prompt, an end-user's test
query, the model's seemingly innocuous response, and, crucially, the model's
internal chain-of-thought, which reveals the underlying malicious intent. Our
benchmark facilitates a new, essential evaluation task: the detection of
deceptive alignment. We demonstrate that D-REX presents a significant challenge
for existing models and safety mechanisms, highlighting the urgent need for new
techniques that scrutinize the internal processes of LLMs, not just their final
outputs.