The full system prompt for Claude 4 has been leaked by X user "Pliny the Liberator" and is now available on GitHub. The document, over 60,000 characters long, sets detailed rules for tone, roles, source handling, and banned content. It controls the model at the system level, before any user prompt is processed. I find it strange that large language models often fail to follow short user instructions, yet seem able to follow complex internal prompts like this one. If you know the reason for that, shoot me an email.
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