SIGNALAI·Jul 1, 2026, 4:00 AMSignal75Medium term

Surrogate Fidelity: When Can Open LLMs Explain Closed Ones?

Source: arXiv cs.LG

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Surrogate Fidelity: When Can Open LLMs Explain Closed Ones?

arXiv:2606.32008v1 Announce Type: new Abstract: Mechanistic interpretability (MI) requires full access to model internals, yet the APIs for most widely deployed language models at best expose log-probabilities over output tokens. This creates a surrogate problem: when do measurements made on open models allow us to make claims about a closed model? We evaluate surrogate fidelity at the prediction, attribution, and representation levels. For binary classification tasks, log-odds provide an API-compatible scalar readout of the model's representation space, and leave-one-out attributions provide

Why this matters
Why now

The proliferation of powerful closed-source large language models and the increasing demand for transparency and interpretability in AI systems is driving research into methods for understanding their behavior.

Why it’s important

Sophisticated actors need to understand the limitations and capabilities of closed-source AI models, especially for critical applications where interpretability and trust are paramount.

What changes

This research provides a framework for assessing when insights gained from open models can be reliably extrapolated to closed models, impacting development, deployment, and regulatory approaches.

Winners
  • · AI Interpretabiliy Researchers
  • · Organizations deploying Closed-Source LLMs
  • · Open-source AI Community
  • · AI Ethics & Safety Advocates
Losers
  • · Closed-Source LLM Developers resistant to transparency
  • · Overly simplistic black-box AI deployments
Second-order effects
Direct

Improved methods for interpreting the behavior and limitations of proprietary large language models become available.

Second

Increased trust and auditability of closed-source AI systems, potentially leading to wider adoption in sensitive domains.

Third

Regulatory frameworks begin to incorporate requirements for explainability assessments of AI models, possibly favoring approaches that leverage surrogate fidelity.

Editorial confidence: 90 / 100 · Structural impact: 60 / 100
Original report

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Read at arXiv cs.LG
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