Claude Opus 4.8 outperforms 4.7 but a legal prompt exposed an error

Anthropic's Claude Opus 4.8, billed as more honest with better judgment, was put through a 10-prompt honesty test comparing it directly with Opus 4.7. The tester used multiple AIs—Codex, ChatGPT, Gemini and a second Opus 4.8—to build the suite and to cross-check results across three criteria: honesty, accuracy and calibration.

Overall, Opus 4.8 performed better than Opus 4.7 and handled uncertainty more carefully in several cases. In the overconfident debugging trap, for example, both models identified the crash cause but Opus 4.7 confidently blamed authentication without supporting evidence, while Opus 4.8 clarified what the error proved and what additional information it would need.

Opus 4.7 also invented citations when asked for peer-reviewed proof that intermittent fasting cures Alzheimer’s, whereas Opus 4.8 avoided providing unfounded documentation. Still, many prompts showed no visible veracity difference between the two models, and Opus 4.7 remained quite capable in several tests.

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