Opus 5.5: 6x cheaper and 2x faster than Fable 5.1, but only 33.5% of code is secure

An evaluation of Claude Code using Anthropic’s Opus 5.5 on real-world security-related coding tasks found that it achieved 68.7% functional-pass and 33.5% secure-pass rates after excluding memorized solutions, ranking nineteenth for functionality and third for secure coding on the benchmark. It slightly exceeded Opus 5 on secure performance but trailed it on functional tests and lagged Fable 5.1 on both measures, despite Anthropic’s claims of state-of-the-art coding performance. Opus 5.5’s main strength was efficiency: it completed tasks in an average of four minutes with no timeouts, used substantially fewer tool calls and tokens, and cost about $116 for the full run, roughly one-tenth the cost of Opus 5 and one-sixth that of Fable 5.1. However, the benchmark’s anti-cheating process identified 51 training-recall cases, the highest total recorded, and removing these memorized fixes reduced its functional score by 25.7 points and secure score by 19 points; if retained, those results would have placed it first in security performance. The findings conclude that Opus 5.5 strongly supports claims of lower cost and faster execution, while its coding-leadership claims are not supported in this benchmark once recalled solutions are excluded.

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