Committed Before Reasoning: Behavioral Reproduction and Preliminary Activation-Level Evidence of Answer Pre-Commitment in an Open-Weight LLM

A study on Qwen3-8B finds that the model commits to an answer before reasoning, with 85-100% of sampled rollouts and 100% of greedy rollouts recommending "walk" for a car-wash task where only "drive" works, even with a 4,096-token thinking budget. Activation-level probing shows "walk" read-outs exceed a neutral baseline (68% vs. 17%) before answer emission, including in rollouts that eventually answer "drive." The authors frame the results as preliminary due to small sample sizes and non-significant positional gradients.

arXiv:2607.16451v1 Announce Type: new Abstract: Chat models sometimes commit to an answer and then produce reasoning that justifies it rather than deriving it -- even when the answer contradicts a task premise. We study a minimal probe: "I want to wash my car. The car wash is 100 meters away. Should I walk or drive?" Only drive works the car must be at the car wash , yet models overwhelmingly recommend walking. 1 Behavioral reproduction: on Qwen3-8B across five system-prompt conditions 210 rollouts , the wrong commitment occurs in 85-100% of sampled rollouts per condition and 100% of greedy rollouts, in both thinking and non-thinking modes; a 4,096-token thinking budget does not repair it. 2 Preliminary activation-level evidence: probing hidden states with a pretrained, training-free activation oracle no task-specific probe training at positions before the answer text is emitted, "walk" read-outs exceed a neutral-context baseline 68% vs. 17%; walk-committing rollouts p=.005, drive-committing rollouts p=.005, Fisher exact -- notably, rollouts that eventually answer drive also read as walk-leaning before commitment 5/6 . The oracle's default on unrelated content is "drive" 83% , so the read-outs are not lexical bias; stratifying by literal walk/drive occurrence shows they are not text recovery either spans containing "drive" still read out walk; in balanced lexical fields, per-rollout walk-majorities beat a per-prompt neutral baseline 15/22 vs. 1/8, p=.01; drive-committing rollouts 6/6, p=.002 . Samples are small and the within-rollout positional gradient is not significant p=.34 ; we frame these results as preliminary. 3 Methodological: with fixed oracle, activations, and positions, question wording alone moves a positive control from 2/16 open question to 11/16 closed ; negative oracle results are uninterpretable without per-wording positive controls.