Trust but Verify: Prover-Verifier Deliberation for Selective LLM Prediction

João Sedoc, Baotong Zhang, Dean Foster

#750 of 2682 · Artificial Intelligence
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Tournament Score
1456±44
10501800
68%
Win Rate
15
Wins
7
Losses
22
Matches
Rating
6/ 10
Significance
Rigor
Novelty
Clarity

Abstract

Reliably knowing when a language model is correct is almost as important as being correct. We introduce prover-verifier deliberation (PVD), an inference-time protocol grounded in interactive proof theory, as a mechanism for selective prediction: the protocol produces both an answer and a structured confidence verdict, allowing a system to report high-confidence answers while abstaining on uncertain cases. In each dialogue, a prover defends a candidate answer through checkable sub-claims while a verifier issues targeted challenges and returns \textsc{Accept}, \textsc{Challenge}, or \textsc{Reject}. Because frozen language models are imperfect provers and verifiers operating over a noisy channel, formal soundness and completeness guarantees do not transfer; instead, we characterize the protocol empirically through its coverage-precision behavior. Our main experiment uses Claude Sonnet 4.6 as prover and Claude Haiku 4.5 as verifier on GPQA Diamond. Questions accepted with no answer revision, which we call Accept + No Change (ANC), are reported as the high-confidence subset; we evaluate this subset by its precision and coverage. ANC separates reliable from unreliable answers, yielding a \sim30pp HC-Prec gap over the non-ANC complement. Robustness experiments with GPT and Gemini pairings show that high HC-Prec can transfer across model families, while verifier strictness and domain competence largely determine the size of the selection gap. On Humanity's Last Exam, weaker prover-verifier pairings can collapse or invert the ANC signal, illustrating a practical failure mode when the verifier operates outside its effective region. Comparisons with self-consistency, universal self-consistency, multi-agent debate, and Reflexion suggest that prover-verifier deliberation supplies a distinct argument-defensibility signal for selective prediction.

AI Impact Assessments

(1 models)

Scientific Impact Assessment: Trust but Verify: Prover-Verifier Deliberation for Selective LLM Prediction

1. Core Contribution

The paper introduces Prover-Verifier Deliberation (PVD), a structured inference-time protocol that produces both an answer and a confidence verdict for selective prediction. Drawing conceptual inspiration from interactive proof systems, PVD assigns asymmetric roles to two LLMs: a prover decomposes its answer into atomic sub-claims, and a verifier issues targeted challenges, ultimately rendering Accept, Challenge, or Reject verdicts. The key selection signal is "Accept + No Change" (ANC) — cases where the prover's answer survives adversarial scrutiny without revision. This is framed not as an accuracy-boosting technique but as a *calibration* mechanism: knowing when to trust an answer versus abstain.

The conceptual bridge from interactive proof theory to practical LLM selective prediction is well-articulated. The authors are careful to note that formal soundness/completeness guarantees do not transfer to frozen LLMs, and they instead characterize the protocol empirically through coverage-precision behavior. This intellectual honesty strengthens the contribution.

2. Methodological Rigor

The experimental design is generally sound. The paper evaluates across two challenging benchmarks (GPQA Diamond and HLE), multiple model pairings (Claude, GPT, Gemini families), and compares against four relevant baselines (Self-Consistency, Universal Self-Consistency, Multi-Agent Debate, Reflexion). The metrics — HC-Prec, HC-Cov, and the Gap — are well-defined and appropriate for the selective prediction framing.

Several aspects deserve praise:

  • The systematic variation of verifier identity while holding the prover fixed (Table 4) cleanly isolates the verifier's contribution.
  • The overlap analysis with SC (Table 6) demonstrates that PVD captures a structurally different signal.
  • The HLE experiments showing gap inversion with weak verifiers (Table 5) are valuable negative results that define the protocol's failure modes.
  • Statistical significance testing with Wilson intervals and Fisher's exact tests (Appendix A.2.2) adds rigor.
  • However, there are notable methodological concerns:

  • GPQA Diamond has only 198 questions, making some domain-specific analyses quite noisy (Biology n=19).
  • The baseline comparisons are not exhaustive — Debate uses a single configuration, and the authors acknowledge this limitation.
  • The SC baseline for GPT-5.4 uses extended thinking (marked with asterisk), making direct comparison difficult.
  • Cost comparisons mix different model families and pricing tiers, complicating fair assessment.
  • 3. Potential Impact

    The practical value proposition is clear: in deployment scenarios where wrong answers carry high costs (medical, legal, financial), a system that reports 84-98% precision on ~43-77% of questions while flagging the rest for human review is genuinely useful. The protocol requires only ~3 LLM calls per question for the basic configuration, making it computationally efficient compared to 8-sample SC.

    The broader architectural insight — that *argument defensibility* is a distinct and informative signal compared to *sample agreement* — is potentially influential. This suggests new directions for combining verification-based and consistency-based confidence signals. The complementarity analysis (Table 6, showing ANC ∩ full-consensus achieving 96.3% precision) points toward practical ensemble strategies.

    The failure mode analysis on HLE, where the ANC signal inverts, provides a ground-truth-free diagnostic for verifier competence. This is practically valuable: a system can monitor its own ANC gap as a meta-calibration signal.

    However, the restriction to multiple-choice benchmarks limits immediate applicability. Open-ended generation, where correctness is ambiguous and sub-claims are harder to evaluate, is the more pressing deployment scenario — and the paper does not address it.

    4. Timeliness & Relevance

    The paper addresses a genuine bottleneck. As LLMs are deployed in higher-stakes settings, the gap between "often correct" and "reliably knows when correct" becomes critical. Most inference-time scaling work focuses on accuracy; selective prediction has been relatively neglected for LLMs. The timing is good — with multiple frontier model families available via API, the cross-family experiments are newly feasible and practically relevant.

    The connection to the growing literature on AI safety and oversight is implicit but important: understanding when models should abstain is foundational for trustworthy deployment.

    5. Strengths & Limitations

    Key Strengths:

  • *Novel and well-motivated framing*: Casting interactive proof structure as a selective prediction mechanism is creative and generates useful empirical insights.
  • *Honest epistemic framing*: The authors explicitly disclaim formal guarantees and characterize everything empirically. The failure mode analysis is as informative as the success cases.
  • *Complementarity demonstration*: Showing that PVD and SC capture orthogonal error classes (Table 6) is the paper's most compelling analytical contribution.
  • *Practical efficiency*: ~3 calls per question for meaningful calibration is deployment-friendly.
  • *Reproducibility*: Code, prompts, and result logs are released.
  • Notable Limitations:

  • *Benchmark scope*: Only English multiple-choice questions with unambiguous correctness criteria. The gap to open-ended or multilingual tasks is large.
  • *Proprietary models only*: All experiments use closed-source APIs, limiting reproducibility and making results sensitive to provider changes.
  • *No learned combination*: The paper uses ANC as a binary signal rather than exploring richer features (number of rounds, challenge types, revision patterns) in a learned selector.
  • *Overall accuracy is not improved*: PVD's full-population accuracy is comparable to single-call baselines. Without implementing the promised "downstream remediation," the end-to-end value proposition remains theoretical.
  • *Small sample sizes*: Many domain breakdowns and complement sets are too small for reliable inference.
  • *No conformal or distribution-free baselines*: The paper acknowledges this gap but it weakens the comparison to the calibration literature.
  • Additional Observations

    The self-deliberation ablation (single model as both prover and verifier) showing a ~15pp reduction in gap is informative but raises questions about what exactly drives the signal — is it the structured decomposition, the adversarial pressure, or the model separation? Disentangling these would strengthen the contribution.

    The "effective verifier" concept is theoretically interesting but remains informal. A more rigorous characterization of when and why the ANC signal works would elevate this from a useful engineering protocol to a deeper scientific contribution.

    Rating:6/ 10
    Significance 6.5Rigor 6Novelty 6.5Clarity 7.5

    Generated May 26, 2026

    Comparison History (22)

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