Claude Opus 4 and Claude Sonnet 4 are Anthropic’s latest hybrid-reasoning language models. The system card explains how the models were trained on a blend of public web data, opted-in user content and proprietary sources, and how they can switch between a quick default mode and a slower “extended thinking” mode for harder problems. The card outlines a battery of safety checks, ranging from single-turn content filters and bias benchmarks to red-team exercises and agentic coding trials. These evaluations informed Anthropic’s decision to release Opus 4 under the stricter AI Safety Level 3 standard and Sonnet 4 under Level 2.
For practitioners the document is more than corporate disclosure: it is a technical manual that signals where the models excel, where guard-rails bite and what deployment obligations follow. Understanding these details helps product teams gauge reliability, tailor prompts and comply with risk policies, while giving end-users a clearer view of why the models may refuse, summarise or slow down in certain scenarios. In short, the card turns abstract assurances of “helpfulness, honesty and harmlessness” into concrete, auditable claims that can be tested in the real world.
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