Claude Fable 5: the agent harness matters more than the frontier model

Before it got yanked, Endor Labs ran Claude Fable 5 through two agent harnesses, Claude Code and Cursor, on 200 real-world vulnerability-fixing tasks inside actual projects. Cursor with Fable 5: 72.6% FuncPass 29.0% SecPass Claude Code with Fable 5: 59.8% FuncPass 19.0% SecPass Both harnesses produced working code. The gap came down to patch completeness. Cursor consistently steered the model to close every vulnerable sink. Claude Code produced working patches, just not always secure ones. Tons of hype around new model releases these days, but the takeaway seems to be that the agent harness matters much more than the model itself. submitted by /u/bugvader25 [link] [comments]Technical Information Security Content & DiscussionRead More