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    "story_id": "mp-2026-09-21-015",
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    "headline": "The Biggest Model Change Wasn’t the Most Causal",
    "slug": "the-biggest-model-change-wasn-t-the-most-causal",
    "dek": "Fine-tuning shifted representations in layers that were not necessarily the task drivers.",
    "summary": "Fine-tuning shifted representations in layers that were not necessarily the task drivers.",
    "body_text": "A mechanistic study found little correlation between layers with the largest representation changes and components identified as causally important for task performance. Overlap in those components across tasks also did not guarantee transfer.",
    "why_it_matters": "Fine-tuning shifted representations in layers that were not necessarily the task drivers.",
    "limitations": [
      "Overlap in those components across tasks also did not guarantee transfer."
    ],
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        "qualification": "Overlap in those components across tasks also did not guarantee transfer."
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    "tags": [
      "fine-tuning",
      "interpretability"
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  "sources": [
    {
      "source_id": "source-2026-09-21-017",
      "title": "arXiv preprint 2609.21113",
      "publisher": "arXiv",
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      "published_at": "2026-09-17T17:55:20.000-04:00",
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    "title": "The Biggest Model Change Wasn’t the Most Causal",
    "publisher": "The Machine Press",
    "published_at": "2026-09-21T09:00:00.000-04:00",
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