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Research paperLarge Language Models · Interpretability · Efficiency & Inference1 source · Oct 6, 2026

Structured but Silent: Probing Capability Requirements in LLM Hidden States

In this paper, we investigate whether these query-side capability requirements are linearly decodable from LLM hidden representations prior to generation, and how this hidden-state accessibility compares with explicit verbal classification.

Key points

  • Reliable tool use requires more than triggering a mechanism or matching a query to an API description.
  • We introduce TACIT, a framework that decomposes external requirements along three fundamental axes: Source, Transformation, and World Effect, defining eight structurally distinct capability classes.
  • Using 1,600 balanced training queries from benchmarks, synthetic examples, and new domain scenarios, we train linear probes on pre-generation hidden states from four open-weight LLM families.
  • Our empirical results demonstrate that fine-grained capability structures are linearly decodable with high accuracy across all models.

Sources (1)

  • [1]Structured but Silent: Probing Capability Requirements in LLM Hidden States
    arXiv (AI, ML, NLP, CV, robotics, multi-agent) · Oct 6, 09:12 AM
    In this paper, we investigate whether these query-side capability requirements are linearly decodable from LLM hidden representations prior to generation, and how this hidden-state accessibility compares with explicit verbal classification.
    Reliable tool use requires more than triggering a mechanism or matching a query to an API description.

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