Claude Opus 5: The System Card

Anthropic has released Claude Opus 5, a mid-tier model pitched as a practical alternative to its more expensive Fable 5. Per LessWrong analyst Zvi Mowshowitz, Opus 5 matches or exceeds Fable's capabilities on most everyday tasks, runs faster, and costs half as much. On specialized work—like cybersecurity—Opus 5 doesn't reach the level of Anthropic's most powerful model, Mythos 5, but it substantially outpaces its predecessor, Opus 4.8. Anthropic also relaxed some safeguards with this release: Opus 5 now permits vulnerability analysis in source code, a change intended to help developers write more secure software. Safety classifiers trigger less than five percent of the time, a dramatic drop from forty-two percent previously.

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