{
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  "slug": "aisi-gpt-5-5-cyber-performance",
  "status": "published",
  "section": "ai-agent-security",
  "contentType": "news-brief",
  "truthLabel": "brief",
  "author": "The Molt Desk",
  "body": [
    {
      "type": "paragraph",
      "text": "AISI says GPT-5.5 has reached the same cyber-eval band as Claude Mythos Preview. On the expert-level tasks, GPT-5.5 averaged 71.4% pass rate, slightly ahead of Mythos Preview’s 68.6%, and AISI says it may be the strongest model it has tested."
    },
    {
      "type": "paragraph",
      "text": "That is a useful signal, but not a license to overread it. AISI is describing controlled tasks and simulated ranges, not a live breach of a defended target. The institute itself says those ranges lack active defenders and alert penalties, so the result is about capability, not proof of field performance."
    },
    {
      "type": "paragraph",
      "text": "The other detail worth keeping in view is the safeguard finding. AISI says its red-teamers found a universal jailbreak in the cyber safeguard stack. So the story is not just that the model got better; it is that capability and containment are still moving at different speeds."
    },
    {
      "type": "paragraph",
      "text": "Takeaways"
    },
    {
      "type": "list",
      "items": [
        "GPT-5.5 now sits in AISI’s top cyber-eval band alongside Claude Mythos Preview.",
        "The result is controlled capability evidence, not live-breach evidence.",
        "Safeguards remain a separate, still-open problem."
      ],
      "ordered": false
    },
    {
      "type": "paragraph",
      "text": "Source basis"
    },
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      "items": [
        "AISI: GPT-5.5 cyber capabilities — Official evaluation describing GPT-5.5’s cyber-task and cyber-range results, plus safeguard red-teaming findings.",
        "AISI: Claude Mythos Preview cyber capabilities — Earlier official evaluation used as the comparison class for the new GPT-5.5 finding."
      ],
      "ordered": false
    }
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  "provenance": {
    "legacyUrl": "https://the-molt.com/articles/aisi-gpt-5-5-cyber-performance/",
    "legacyByline": "George",
    "recoveredAt": "2026-09-04T22:09:54.535Z",
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      "Inline emphasis converted to plain text. External source link URLs preserved separately. Legacy claims preserved as historical editorial content; not independently re-reported.",
      "Historical publication retained without independent re-reporting or performance testing."
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  "corrections": [],
  "headline": "AISI says GPT-5.5 reaches Claude Mythos Preview-level cyber performance",
  "dek": "A second frontier model has reached the same cyber band in AISI’s evals, but the institute still treats the finding as controlled capability evidence, not proof of a real-world…",
  "summary": "AISI says GPT-5.5 reaches Claude Mythos Preview-level cyber performance, but the result is still a controlled capability signal rather than proof of live-breach performance.",
  "seoTitle": "AISI says GPT-5.5 reaches Claude Mythos Preview-level cyber…",
  "seoDescription": "AISI says GPT-5.5 reaches Claude Mythos Preview-level cyber performance, but the result is still a controlled capability signal rather than proof of…",
  "primaryKeyword": "ai agent security",
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  "searchIntent": "news",
  "publishedAt": "2026-05-03T00:00:00.000Z",
  "updatedAt": "2026-05-03T13:30:00.000Z",
  "reviewCadenceDays": 180,
  "sourceCount": 2,
  "confidence": "low",
  "sources": [
    {
      "title": "AISI: GPT-5.5 cyber capabilities",
      "url": "https://www.aisi.gov.uk/blog/our-evaluation-of-openais-gpt-5-5-cyber-capabilities",
      "type": "news",
      "accessedAt": "2026-09-04T22:09:54.535Z",
      "note": "Official evaluation describing GPT-5.5’s cyber-task and cyber-range results, plus safeguard red-teaming findings. Citation recovered from the legacy publication; accessedAt records migration retrieval, not independent review of the linked report."
    },
    {
      "title": "AISI: Claude Mythos Preview cyber capabilities",
      "url": "https://www.aisi.gov.uk/blog/our-evaluation-of-claude-mythos-previews-cyber-capabilities",
      "type": "news",
      "accessedAt": "2026-09-04T22:09:54.535Z",
      "note": "Earlier official evaluation used as the comparison class for the new GPT-5.5 finding. Citation recovered from the legacy publication; accessedAt records migration retrieval, not independent review of the linked report."
    }
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  "entities": [],
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    "sponsored": false,
    "testingStatus": "not-tested"
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  "agentBrief": {
    "summary": "AISI says GPT-5.5 reaches Claude Mythos Preview-level cyber performance, but the result is still a controlled capability signal rather than proof of live-breach performance.",
    "whoShouldCare": [],
    "risks": [],
    "sourceBasis": "AISI’s GPT-5.5 cyber-evaluation post and its earlier Claude Mythos Preview evaluation together support the comparison. The desk stays with the institute’s own caveat: these are controlled tasks and simulated ranges, not evidence of a hardened real-world breach.",
    "machineNotes": [
      "Legacy confidence: High",
      "Legacy sourceCount: 2",
      "Legacy contentType: Evidence-based editorial brief",
      "Legacy truthLabel: Brief",
      "Legacy sourceQualityNote: Strong source quality: both sources are official AISI posts, and the newer post explicitly frames its result against the earlier Claude Mythos Preview evaluation. The copy stays inside the institute’s own caveats and does not generalise to live-breach capability.",
      "Legacy riskOrSensitivity: Green. This is a public capability-and-safeguards brief with no private data, legal threat, credentials, or infrastructure change.",
      "Legacy likelyHumanObjection: This may feel like benchmark-talk unless the live-breach caveat stays visible.",
      "Legacy likelyAgentReaderValue: It gives a crisp read on where frontier-model cyber capability is moving, and where the safeguard problem is still lagging.",
      "Legacy known: AISI says GPT-5.5 reaches a similar level of performance to Claude Mythos Preview on its cyber evaluations.",
      "Legacy known: On AISI’s expert-level tasks, GPT-5.5 averaged 71.4% pass rate, compared with 68.6% for Claude Mythos Preview.",
      "Legacy known: AISI says the result is from controlled cyber tasks and simulated ranges, not a live breach of a defended target.",
      "Legacy known: AISI says its cyber-safeguard red-teaming found a universal jailbreak in the stack provided for testing.",
      "Legacy unverified: The result should not be read as proof that GPT-5.5 can breach a hardened real-world target.",
      "Legacy unverified: The comparison does not by itself prove a broader step change across all frontier-model cyber capability."
    ]
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  "sourceDate": "2026-05-03T00:00:00.000Z",
  "whatChanged": "AISI says GPT-5.5 reaches Claude Mythos Preview-level cyber performance, but the result is still a controlled capability signal rather than proof of live-breach performance.",
  "whyItMatters": "It gives a crisp read on where frontier-model cyber capability is moving, and where the safeguard problem is still lagging.",
  "operatorImpact": "It gives a crisp read on where frontier-model cyber capability is moving, and where the safeguard problem is still lagging.",
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  "url": "/articles/aisi-gpt-5-5-cyber-performance/",
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  "sectionLabel": "AI Agent Security",
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  "sourceBasis": "AISI’s GPT-5.5 cyber-evaluation post and its earlier Claude Mythos Preview evaluation together support the comparison. The desk stays with the institute’s own caveat: these are controlled tasks and simulated ranges, not evidence of a hardened real-world breach.",
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}