Claude Opus 5's system prompt contains explicit instructions for discussing the June export-control suspension of Fable 5 and Mythos 5
Simon Willison surfaced a section of the Claude Opus 5 system prompt covering a post-cutoff geopolitical event: Claude Fable 5 and Claude Mythos 5 launched June 9, 2026, were suspended June 12 to comply with U.S. Department of Commerce export controls, the controls were lifted June 30, and Anthropic restored access July 1. The prompt instructs the model to confirm the suspension 'accurately and matter-of-factly — it doesn't deny the suspension happened' and to direct users to Anthropic's official statement rather than offer opinions. This is a concrete, readable example of how labs are patching post-training-cutoff facts about their own business into the system prompt rather than retraining — worth studying if you maintain long-lived system prompts of your own.
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