Model-Adaptive Tool Necessity Reveals the Knowing-Doing Gap in LLM Tool Use

In three linesarXiv paper showing LLMs exhibit a knowing-doing gap in tool use: recognition of tool necessity vs. actual invocation diverge. Testing 4 models on arithmetic and factual QA reveals 26.5-54% mismatches. Hidden state probing shows cognition and action signals become nearly orthogonal in late layers, with most failures at the cognition-to-action transition, not in recognition itself.

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