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Reasoning Models Know When They're Right: Probing Hidden States for Self-Verification

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arxiv 2504.05419 v1 pith:SKFNQR3R submitted 2025-04-07 cs.AI cs.CL

classification cs.AIcs.CL
keywords reasoningmodelscorrectnessanswersintermediateanswerduringencode
verification ladder T0 review T1 audit T2 compute T3 formal
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Reasoning models have achieved remarkable performance on tasks like math and logical reasoning thanks to their ability to search during reasoning. However, they still suffer from overthinking, often performing unnecessary reasoning steps even after reaching the correct answer. This raises the question: can models evaluate the correctness of their intermediate answers during reasoning? In this work, we study whether reasoning models encode information about answer correctness through probing the model's hidden states. The resulting probe can verify intermediate answers with high accuracy and produces highly calibrated scores. Additionally, we find models' hidden states encode correctness of future answers, enabling early prediction of the correctness before the intermediate answer is fully formulated. We then use the probe as a verifier to decide whether to exit reasoning at intermediate answers during inference, reducing the number of inference tokens by 24\% without compromising performance. These findings confirm that reasoning models do encode a notion of correctness yet fail to exploit it, revealing substantial untapped potential to enhance their efficiency.

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Cited by 13 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

  1. Multi-Head Latent Control: A Unified Interface for LLM Agent Decision Making

    cs.CL 2026-07 conditional novelty 6.0 of 10

    Hidden-state traces of frozen LLMs/VLMs can be read by lightweight trained heads to predict when to defer, clarify, call tools, or abstain, cutting routed inference cost 27–90%.

  2. LLMs as a Jury: Cross-Model Consensus Can Outperform Process Reward Models for LLM Reasoning

    cs.LG 2026-07 conditional novelty 6.0 of 10

    Cross-model answer agreement is a free Best-of-N verifier that matches trained process reward models and is predicted by a parameter-free law from three panel statistics.

  3. Learning More from Less: Unlocking Internal Representations for Benchmark Compression

    cs.AI 2026-01 conditional novelty 6.0 of 10

    Using aligned hidden states from ten LLMs to select a small representative question set lets RepCore estimate full-benchmark accuracy and rankings more accurately than output-only methods.

  4. Rethinking LLM Parametric Knowledge as Post-retrieval Confidence for Dynamic Retrieval and Reranking

    cs.IR 2025-09 conditional novelty 6.0 of 10

    Shifts in an LLM's hidden-state confidence, before and after a retrieved context, are used as a preference signal to fine-tune a reranker and to trigger retrieval only when initial confidence is low.

  5. Real-Time Progress Prediction in Reasoning Language Models

    cs.LG 2025-06 conditional novelty 6.0 of 10

    Fine-tuned reasoning models and linear probes can emit estimates of normalized trace position, used here as a progress proxy, reaching 0.161 MAE on math traces, though simple length baselines capture most of the signal.

  6. Exploring and Exploiting the Inherent Efficiency within Large Reasoning Models for Self-Guided Efficiency Enhancement

    cs.AI 2025-06 conditional novelty 6.0 of 10

    Large reasoning models already contain the ability to reason concisely; steering their internal activations or rewarding brevity can cut reasoning length by up to half without hurting accuracy.

  7. The Geometries of Truth Are Orthogonal Across Tasks

    cs.LG 2025-06 conditional novelty 6.0 of 10

    Linear probes of LLM hidden states that predict answer correctness are task-specific, with near-zero directional overlap across tasks, and no multi-task trick fixes this.

  8. CoRE: Enhancing Metacognition with Label-free Self-evaluation in LRMs

    cs.LG 2025-07 conditional novelty 5.0 of 10

    A training-free and label-free detector of cyclic hidden-state patterns triggers early exit during chain-of-thought reasoning, reducing token length while mostly preserving or improving accuracy.

  9. Deciphering Trajectory-Aided LLM Reasoning: An Optimization Perspective

    cs.CL 2025-05 conditional novelty 5.0 of 10

    Reasoning trajectories are formalized as pseudo-gradient descent on LLM parameters, making LLM reasoning training a MAML-style meta-learning problem.

  10. Training-Free versus Training-Based Intent Classification in LLMs: Accuracy, Robustness, and Failure Modes

    cs.CL 2026-08 conditional novelty 4.0 of 10

    Statistical classifiers built on LLM activation norms and coordinates match or beat trained MLP heads on coarse intent routing and resist camouflage better, while MLPs win on fine-grained subfield distinctions.

  11. A Comprehensive Survey on Trustworthiness in Reasoning with Large Language Models

    cs.CL 2025-09 conditional novelty 4.0 of 10

    A structured literature survey concluding that reasoning capabilities do not automatically make LLMs more trustworthy and can introduce new vulnerabilities in safety, robustness, and privacy.

  12. Wait, We Don't Need to "Wait"! Removing Thinking Tokens Improves Reasoning Efficiency

    cs.CL 2025-06 conditional novelty 4.0 of 10

    Suppressing "Wait"-like reflection tokens at decode time reduces reasoning token counts by 27-51% across five R1-style model families, with mixed accuracy effects.

  13. Towards Concise and Adaptive Thinking in Large Reasoning Models: A Survey

    cs.AI 2025-07 conditional novelty 3.0 of 10

    A comprehensive review that categorizes methods for shortening and adaptively triggering chain-of-thought reasoning in large language models.

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