AI Signal 571
Quoting Claude Opus 5 system prompt
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Illustration only Photo by Yogesh Phuyal on Unsplash
Simon Willison quotes a Claude Opus 5 system prompt that instructs the model on how to handle the temporary suspension and restoration of access to Claude Fable 5 and Mythos 5 due to US export controls.
This shows how system prompts are used to inject post-training knowledge into models. For engineers, it highlights the practice of patching model behavior via prompts rather than retraining, and the need to keep such prompts updated as facts change.
Written by elseif from the cluster below · every claim links back to a sourceThe three things worth knowing
The system prompt includes a notice about the export-control suspension because it occurred after the model's training cutoff.
The prompt instructs the model to confirm the suspension accurately and treat it as a current political topic without personal opinion.
The model is directed to check for newer information when searching is available and otherwise point to Anthropic's statement.
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