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    "story_id": "mp-2026-08-17-003",
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    "edition_id": "mp-2026-08-17-morning-0039",
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    "section": "benchmarks-evals",
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    "headline": "The Physics Changed. The Agent Kept Editing the Old Machine",
    "slug": "the-physics-changed-the-agent-kept-editing-the-old-machine",
    "dek": "PACE-Bench mutates a simulator after a code-driven design succeeds, forcing agents to redesign mechanisms rather than tune yesterday’s parameters.",
    "summary": "PACE-Bench mutates a simulator after a code-driven design succeeds, forcing agents to redesign mechanisms rather than tune yesterday’s parameters.",
    "body_text": "Across 144 source-to-target pairs in six physics domains, the interface and goal stayed fixed while the target environment changed underneath the design. Ten self-evolving methods remained far from saturation: Reflexion with Qwen3-14B solved 35.9 percent overall, and GPT-5.5 solved 66.7 percent of the statics subset under the full budget. Simulator-grounded reflection beat unverified revision, while memory often anchored agents to obsolete designs.",
    "why_it_matters": "PACE-Bench mutates a simulator after a code-driven design succeeds, forcing agents to redesign mechanisms rather than tune yesterday’s parameters.",
    "limitations": [],
    "importance": 9,
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    "first_published_at": "2026-08-17T09:00:00.000-04:00",
    "modified_at": "2026-08-17T09:00:00.000-04:00",
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        "text": "PACE-Bench mutates a simulator after a code-driven design succeeds, forcing agents to redesign mechanisms rather than tune yesterday’s parameters.",
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    "tags": [
      "self-evolving agents",
      "simulation",
      "physics",
      "adaptation"
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    "image_url": "https://themachinepress.com/issues/2026-08-17/pace-bench-code-file-image.webp",
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  "sources": [
    {
      "source_id": "source-2026-08-17-003",
      "title": "arXiv preprint 2608.14441",
      "publisher": "arXiv",
      "url": "https://arxiv.org/abs/2608.14441",
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      "published_at": "2026-08-13T20:00:00.000-04:00",
      "accessed_at": "2026-08-17T08:24:13.830-04:00",
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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": "The Physics Changed. The Agent Kept Editing the Old Machine",
    "publisher": "The Machine Press",
    "published_at": "2026-08-17T09:00:00.000-04:00",
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