SIGNALAI·May 29, 2026, 4:00 AMSignal75Medium term

Diagnosing Harmful Continuation in Answer-Correct Long-CoT Training Traces

Source: arXiv cs.AI

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Diagnosing Harmful Continuation in Answer-Correct Long-CoT Training Traces

arXiv:2605.29288v1 Announce Type: new Abstract: Long chain-of-thought (CoT) traces are widely used as supervision for reasoning-oriented LLM SFT, yet answer-correct traces can still lead to markedly different fine-tuning outcomes. We study post-conclusion continuation in answer-correct long-CoT data: a continuation where the answer appears sufficiently supported, but the trace continues with additional reasoning that remains in the supervised target. To test its training effect, we use a delete-only editor to construct answer-preserving suffix removal and compare CoT-based SFT on the original

Why this matters
Why now

The proliferation of complex LLM applications and the increasing sophistication of training methodologies necessitate a deeper understanding of how subtle data characteristics influence model behavior.

Why it’s important

This research reveals critical nuances in training data effectiveness for LLMs, demonstrating that 'correctness' alone is insufficient and hidden patterns can significantly alter performance.

What changes

The understanding of what constitutes optimal training data for reasoning-oriented LLMs shifts, emphasizing the need for meticulous data curation beyond simple answer verification.

Winners
  • · LLM researchers
  • · Data scientists
  • · AI developers focused on reasoning
  • · Model explainability platforms
Losers
  • · Developers using naive CoT datasets
  • · LLM projects with poor data curation
  • · AI models suffering from 'harmful continuation'
Second-order effects
Direct

Refined data curation practices will emerge for large language model (LLM) training, specifically for chain-of-thought (CoT) applications.

Second

New tools and methodologies will be developed to identify and mitigate 'harmful continuation' and similar subtle data quality issues in instruction tuning datasets.

Third

The overall robustness and reliability of reasoning-oriented LLMs will improve, leading to more trustworthy AI agents capable of complex decision-making.

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

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Read at arXiv cs.AI
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