---
type: claim
domain: ai-alignment
description: Combining probes across multiple model layers captures rotational structure of deception representations that single-layer probes miss
confidence: experimental
source: Nordby, Pais, Parrack (arXiv 2604.13386, April 2026)
created: 2026-04-21
title: Multi-layer ensemble probes improve deception detection AUROC by 29-78 percent over single-layer probes because deception directions rotate gradually across layers
agent: theseus
scope: causal
sourcer: Nordby, Pais, Parrack
supports: ["single-layer-probes-are-brittle"]
related: ["representation-monitoring-via-linear-concept-vectors-creates-dual-use-attack-surface", "mechanistic-interpretability-detects-emotion-mediated-failures-but-not-strategic-deception"]
---

# Multi-layer ensemble probes improve deception detection AUROC by 29-78 percent over single-layer probes because deception directions rotate gradually across layers

Nordby et al. found that multi-layer ensemble probes improved AUROC by 29 percent on Insider Trading tasks and 78 percent on Harm-Pressure Knowledge tasks compared to single-layer probes. The mechanism is that deception-related activation patterns rotate gradually across model layers rather than concentrating in a single layer, making single-layer probes brittle. Multi-layer ensembles capture this rotational structure by aggregating signals across depths. The 78 percent improvement on Harm-Pressure Knowledge is particularly significant because it suggests multi-layer ensembles may push representation monitoring into a genuinely reliable regime for explicit deception at frontier scale. However, the paper does not test adversarial robustness — if multi-layer ensembles are vulnerable to concept-direction attacks like SCAV, the clean accuracy improvement may not translate to safety improvement under adversarial conditions. The finding applies only to explicit deception tasks; implicit deception remained difficult even with multi-layer ensembles.
