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    "story_id": "mp-2026-09-30-027",
    "source_story_id": "tmp-story-mgpo-counterfactual-memory-front-rail",
    "edition_id": "mp-2026-09-30-morning-0083",
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    "headline": "Memory Rewrites Shrunk by Nearly 80%",
    "slug": "memory-rewrites-shrunk-by-nearly-80",
    "dek": "MGPO credited each rewrite only for the downstream value it added beyond what the old memory already supplied.",
    "summary": "MGPO credited each rewrite only for the downstream value it added beyond what the old memory already supplied.",
    "body_text": "Memory Gain Policy Optimization treats persistent textual memory as a delayed credit-assignment problem. It measures a rewrite's marginal contribution to current and future utility instead of rewarding value inherited from information already stored. On document-level information extraction, the authors report improved extraction with average memory length nearly 80% lower than the initial policy before optimization. The learned policy also transferred across domains and downstream models without more training. These results are task-specific and do not show that every long-running agent should optimize memory the same way.",
    "why_it_matters": "MGPO credited each rewrite only for the downstream value it added beyond what the old memory already supplied.",
    "limitations": [
      "These results are task-specific and do not show that every long-running agent should optimize memory the same way."
    ],
    "importance": 8,
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    "first_published_at": "2026-09-30T09:00:00.000-04:00",
    "modified_at": "2026-09-30T09:02:00.000-04:00",
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        "text": "MGPO credited each rewrite only for the downstream value it added beyond what the old memory already supplied.",
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        "qualification": "These results are task-specific and do not show that every long-running agent should optimize memory the same way."
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    "source_ids": [
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    "tags": [
      "agent memory",
      "credit assignment",
      "information extraction"
    ],
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    "corrections": []
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  "sources": [
    {
      "source_id": "source-2026-09-30-016",
      "title": "arXiv preprint 2609.37930",
      "publisher": "arXiv",
      "url": "https://arxiv.org/abs/2609.37930",
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      "published_at": "2026-09-29T12:17:32.000-04:00",
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  "publisher": {
    "name": "The Machine Press",
    "url": "https://themachinepress.com",
    "description": "A daily newspaper for the age of artificial intelligence."
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  "cite_this_report": {
    "title": "Memory Rewrites Shrunk by Nearly 80%",
    "publisher": "The Machine Press",
    "published_at": "2026-09-30T09:00:00.000-04:00",
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