Pith Number

pith:BQNNVBBJ

pith:2026:BQNNVBBJ34AFQVJ6U75OZELHZJ

not attested not anchored not stored refs pending

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

Chung-En Sun, Ge Yan, Linbo Liu, Tsui-Wei Weng, Zimo Wang

LLM agents already encode whether a tool is needed in their hidden states before generating any output.

arxiv:2605.09252 v2 · 2026-05-10 · cs.CL

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\usepackage{pith}
\pithnumber{BQNNVBBJ34AFQVJ6U75OZELHZJ}

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Record completeness

1 Bitcoin timestamp

2 Internet Archive

3 Author claim open · sign in to claim

4 Citations open

5 Replications open

✓ Portable graph bundle live · download bundle · merged state

The bundle contains the canonical record plus signed events. A mirror can host it anywhere and recompute the same current state with the deterministic merge algorithm.

Claims

C1strongest claim

tool necessity is linearly decodable from the pre-generation representation with AUROC 0.89--0.96 across six models, substantially exceeding the model's own verbalized reasoning.

C2weakest assumption

The linear probe trained on hidden states from the When2Tool benchmark will generalize to new tasks and models without substantial degradation or task-specific artifacts.

C3one line summary

LLMs encode tool necessity in pre-generation hidden states at AUROC 0.89-0.96, enabling Probe&Prefill to reduce tool calls 48% with 1.7% accuracy loss, outperforming prompt and reasoning baselines.

Formal links

2 machine-checked theorem links

Receipt and verification

First computed	2026-05-22T01:03:20.038088Z
Builder	pith-number-builder-2026-05-17-v1
Signature	Pith Ed25519 (`pith-v1-2026-05`) · public key
Schema	pith-number/v1.0

Canonical hash

0c1ada8429df0058553ea7faec9167ca61b65e1916dfdda3830ff08938747085

Aliases

arxiv: 2605.09252 · arxiv_version: 2605.09252v2 · doi: 10.48550/arxiv.2605.09252 · pith_short_12: BQNNVBBJ34AF · pith_short_16: BQNNVBBJ34AFQVJ6 · pith_short_8: BQNNVBBJ

Agent API

Resolver JSON Graph JSON Events JSON Schema Signing key

Verify this Pith Number yourself

curl -sH 'Accept: application/ld+json' https://pith.science/pith/BQNNVBBJ34AFQVJ6U75OZELHZJ \
  | jq -c '.canonical_record' \
  | python3 -c "import sys,json,hashlib; b=json.dumps(json.loads(sys.stdin.read()), sort_keys=True, separators=(',',':'), ensure_ascii=False).encode(); print(hashlib.sha256(b).hexdigest())"
# expect: 0c1ada8429df0058553ea7faec9167ca61b65e1916dfdda3830ff08938747085

Canonical record JSON

{
  "metadata": {
    "abstract_canon_sha256": "99cf9536e1412fc5ddbb1e5237a7790d01959c8a3d3582c5cbc580429ec1a4a7",
    "cross_cats_sorted": [],
    "license": "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",
    "primary_cat": "cs.CL",
    "submitted_at": "2026-05-10T01:37:40Z",
    "title_canon_sha256": "c8e106fb54f734422ae3421a324836d082fe177bb5f4288476ca9d9e935ce317"
  },
  "schema_version": "1.0",
  "source": {
    "id": "2605.09252",
    "kind": "arxiv",
    "version": 2
  }
}