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Opus 4.8 runs leaked Claude Fable 5 prompt

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Opus 4.8 runs leaked Claude Fable 5 prompt
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// 3h agoSECURITY INCIDENT

Opus 4.8 runs leaked Claude Fable 5 prompt

A user on X reported that the system prompt for Anthropic's unreleased Claude Fable 5 model was leaked. Someone reportedly ran this leaked system prompt on an Opus 4.8 model and claimed the resulting output was approximately 90% similar to the real Claude Fable 5 model.

// ANALYSIS

The leak of a flagship model's system prompt highlights significant security challenges in protecting intellectual property for AI labs. It highlights the critical role system prompts play in defining model behavior and output quality, suggests that Opus 4.8 is capable of replicating newer model behaviors when provided with the right instructions, and raises concerns about internal security and prompt protection mechanisms at AI companies.

// TAGS
anthropicclaude-fable-5opus-4.8leaksystem-promptsecurity

DISCOVERED

3h ago

2026-06-15

PUBLISHED

3h ago

2026-06-15

RELEVANCE

8/ 10

AUTHOR

codewithimanshu