Agents & InferenceSimon Willison

Quoting Claude Opus 5 system prompt

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Summary A

Anthropic is now baking post-training-cutoff current events directly into system prompts — here specifically instructing the model on how to accurately handle a real export-control suspension that briefly took two Claude models offline. If you're building on Claude, expect the system prompt to carry factual "ground truth" overrides for events the weights don't know about, which means your own prompt injection and RAG strategies need to account for Anthropic silently shaping the model's factual behavior on recent topics.