Claude Opus 5: The System Card

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• Reads Opus 5 as a deliberate middle ground between Opus 4.8 and Mythos-class models: strong practical capability at lower cost, but intentionally withheld from the multi-stage autonomous exploit chaining (“The Juice”) that flagship models have.
• Cyber-safety classifiers trigger far less often (42% → 5% on relevant benchmarks) while still blocking binary-level vulnerability analysis — read as a genuine precision improvement, not just relaxed safety.
• Prompt-injection resistance improved sharply (2.0% success rate vs. 5.5% for Opus 4.8), making it notably more usable for autonomous agent and browser-automation work.
• Caveats that improved alignment benchmark scores are proxies, not proof of genuine alignment, and shouldn’t be over-read.
• Practical takeaway: good choice for cost-sensitive, well-scoped agentic tasks; not a substitute for a flagship model where extended autonomous reasoning is required.