{"data":{"id":"b93994b9-9cb4-4c47-93bd-790f5cc01dc8","title":"Sonnet 5 vs Fable 5: reliable versus security-forward, not better versus worse | Endor Labs","summary":"Endor Labs compares Sonnet 5 and Fable 5 on its Agent Security League, running each model under Cursor and Claude Code on the same 200-task dataset. After removing cheating and timeout confounds, Sonnet 5 keeps a FuncPass edge on Claude Code (about 10.5 points), while Fable 5 leads on SecPass on both harnesses (19.1 points on Cursor, 3.6 points on Claude Code). The authors conclude the models trade off reliability and thoroughness against security-forward results rather than one being simply better.","solution":"N/A -- no mitigation discussed in source.","labels":["research","industry"],"sourceUrl":"https://www.endorlabs.com/learn/sonnet-5-vs-fable-5-reliable-versus-security-forward-not-better-versus-worse","publishedAt":"2026-10-12T15:59:35.000Z","cveId":null,"cweIds":null,"cvssScore":null,"cvssSeverity":null,"severity":"info","attackType":[],"issueType":"news","affectedPackages":null,"affectedPackageNames":null,"affectedPackageRefs":null,"affectedVendors":["Anthropic","OpenAI"],"affectedVendorsRaw":["Claude Sonnet 5","Fable 5","Cursor","Claude Code"],"classifierModel":"claude-haiku-5-5","classifierPromptVersion":"v4","summaryPromptVersion":"v2","headline":null,"headlinePromptVersion":null,"cvssVector":null,"attackVector":null,"attackComplexity":null,"privilegesRequired":null,"userInteraction":null,"exploitMaturity":null,"epssScore":null,"epssCheckedAt":null,"kevDateAdded":null,"advisoryAliases":null,"affectedPackagesSource":null,"affectedPackagesCheckedAt":null,"patchAvailable":null,"disclosureDate":"2026-10-12T15:59:35.000Z","capecIds":null,"crossRefCount":0,"attackSophistication":"moderate","impactType":null,"aiComponentTargeted":null,"llmSpecific":true,"classifierConfidence":0.7,"researchCategory":null,"atlasIds":null}}