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Present but Hard to Read: Probing Latent Reasoning with Minimal Pairs

Aur Shalev Merin · 2026 · arXiv (Cornell University)

DOI: 10.48550/arxiv.2610.28498 · cited by 0 works (OpenAlex) · open-access PDF

Japanese

私たちは、同じシグナップモデルOuro-1.4Bと標準トランスフォーマーQwen2.5-1.5Bで、同じシグナップモデルOuro-1.4Bからコピーされた数字でこれをテストします。答えが始まるモデルの状態を読み、値が欠けているという証拠として失敗した探査をとります。 答えが始まる場所でのみ異なったプロンプトを比較すると、それは最後のプロンプトトトークンに存在することを示します(読み取るところは約0.9)。 問題の場所で1つのプロンプトを見る探査機は、通常の設定では、ほとんど読まない: 0.36 in Ouroと0.19 in Qwenで、5249のトレーニング質問の後でさえも。 数字の変化は、混合するためのシグナップのための

Machine translation (Meta M2M100); the English original follows.

Abstract

Probing studies of latent reasoning often read a model's state where the answer begins and take a failed probe as evidence that a value is absent. We test this with a digit copied from the question, in the looped model Ouro-1.4B and the standard transformer Qwen2.5-1.5B. Comparing prompts that differ only in that digit shows it is present at the last prompt token, in a code shared across questions (readout about 0.9). A probe that sees one prompt at a time, the usual setting, barely reads it: 0.36 in Ouro and 0.19 in Qwen even after 5,249 training questions. The digit's change is small rather than crowded: random noise lands on equally busy directions, while a random word in its place moves the state far more and is readable. Since every varied token leaves a trace, a successful probe is ambiguous too. We give a protocol, including a synthetic null for generic mixing, for testing computed values against copies and mixtures of the inputs. In pre-registered studies of two-step problems it finds a small signal for the unwritten intermediate a+b just before Ouro writes the answer's last digit, and its sign follows the operation, though mixing alone produces much of that sign-following part. Holding that value at another problem's from the first loop on does not move the written digit toward the other problem's, while the same patch of the answer does: the value is readable but not used.

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Topics: Security token, Computer science, Value (mathematics), Sign (mathematics), Arithmetic, State (computer science)

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