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The Unreasonable Effectiveness of Reasonless Intermediate Tokens (arxiv.org)
4 points by YeGoblynQueenne on May 21, 2025 | hide | past | pdf | 1 comment on HN

In plain words: To test whether reasoning-trace words matter, scientists trained models from scratch on problems with step-by-step traces, then scrambled the middle steps so they no longer fit the problem. The scrambled versions solved problems as well as honest ones, and handled new problem types better.

Abstract · Beyond Semantics: The Unreasonable Effectiveness of Reasonless Intermediate Tokens

Recent impressive results from large reasoning models have been interpreted as a triumph of Chain of Thought (CoT), and especially of the process of training on CoTs sampled from base LLMs in order to help find new reasoning patterns. While these traces certainly seem to help model performance, it is not clear how they influence it, with some works ascribing semantics to them and others cautioning against relying on them as transparent and faithful proxies of the model's internal computational process. To systematically investigate the role of end-user semantics of derivational traces, we set up a controlled study where we train transformer models from scratch on formally verifiable reasoning traces and the solutions they lead to. We notice that, despite gains over the solution-only baseline, models trained on entirely correct traces can still produce invalid reasoning traces even when arriving at correct solutions. More interestingly, our experiments also show that models trained on corrupted traces, whose intermediate reasoning steps bear no relation to the problem they accompany, perform similarly to those trained on correct ones, and even generalize better on out-of-distribution tasks. We also study the effect of GRPO-based RL post-training on trace validity, noting that while solution accuracy increases, this is not accompanied by improvements in trace validity. Finally, we examine whether reasoning-trace length reflects inference-time scaling and find that trace length is largely agnostic to the underlying computational complexity of the problem being solved. These results challenge the assumption that intermediate tokens or ``Chains of Thought'' reflect or induce predictable reasoning behaviors and caution against anthropomorphizing such outputs or over-interpreting them (despite their mostly seemingly forms) as evidence of human-like or algorithmic behaviors in language models.

Karthik Valmeekam, Vardhan Palod, Kaya Stechly, Atharva Gundawar, Subbarao Kambhampati
arXiv:2505.13775 · cs.LG, cs.AI · submitted May 19, 2025 · updated May 25, 2026
abstract · pdf · html · Published in Transactions on Machine Learning Research (TMLR)

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Also discussed: May 2025 (138 points, 66 comments) · May 2025 (2 points, 0 comments)

I asked ChatGPT to restate this in more laymen's terms (posted below) and I am not to surprised at the answer.

"Lately, some AI models have shown impressive abilities to solve complex problems, and many people credit this to a method called Chain of Thought (CoT), where the model is trained to think through steps like a human might. In this paper, we take a closer look at that idea to see if it's really what's driving better performance.

We focus on the model’s step-by-step thinking (the words it generates along the way) — often treated like human "thoughts" — and examine whether these actually help the model solve problems more accurately. To test this, we train AI models using clean, correct step-by-step reasoning paths and final answers, all based on a known solving method (A* search). This lets us check both the final answers and the reasoning steps to see how they relate.

Interestingly, we find that even when a model gives the right answer, its reasoning steps can still be wrong or messy. To go further, we even train models using completely random and incorrect reasoning steps — and surprisingly, they still perform about the same, and sometimes even better, than those trained on correct steps.

This suggests that the step-by-step "thoughts" the model shows aren’t as meaningful or reliable as many assume. In short, just because a model looks like it’s reasoning through a problem doesn’t mean it actually is — and we should be careful not to treat its outputs as if it thinks like a human or follows strict logic."