SIGNALAI·May 22, 2026, 4:00 AMSignal75Short term

LLM Agents Already Know When to Call Tools -- Even Without Reasoning

Source: arXiv cs.CL

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LLM Agents Already Know When to Call Tools -- Even Without Reasoning

arXiv:2605.09252v2 Announce Type: replace Abstract: Tool-augmented LLM agents tend to call tools indiscriminately, even when the model can answer directly. Each unnecessary call wastes API fees and latency, yet no existing benchmark systematically studies when a tool call is actually needed. We propose When2Tool, a benchmark of 18 environments (15 single-hop, 3 multi-hop) spanning three categories of tool necessity -- computational scale, knowledge boundaries, and execution reliability -- each with controlled difficulty levels that create a clear decision boundary between tool-necessary and to

Why this matters
Why now

The proliferation of advanced LLM agents necessitates more efficient and cost-effective tool utilization, as current models often make unnecessary API calls.

Why it’s important

This development improves the efficiency and reduces the operational cost of AI agents, making them more practical for real-world applications.

What changes

LLM agents can now more intelligently decide when external tools are genuinely required, leading to optimized performance and resource consumption.

Winners
  • · AI Agent developers
  • · Cloud API providers (who charge for usage)
  • · Enterprises deploying LLM agents
Losers
  • · Inefficient LLM agent architectures
Second-order effects
Direct

Reduced API costs and latency for tool-augmented LLM agents.

Second

Accelerated deployment and adoption of sophisticated AI agent systems across various industries.

Third

Enhanced overall economic viability and scalability of agentic AI solutions, potentially leading to faster automation of complex tasks.

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

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Read at arXiv cs.CL
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