What was Anthropic's original plan for Claude Fable 5?

Anthropic had planned to invisibly degrade Claude Fable 5's performance for users trying to train competing AI models, but reversed course after backlash from the research community.

What is the remaining controversy around Fable 5?

Claude Fable 5 requires data retention to run its new safety classifiers, storing prompts and outputs for up to 30 days, and up to two years if policy violations are flagged. All other Claude models operate under zero-data-retention rules, and Microsoft is restricting Fable 5 internally in GitHub Copilot because of this requirement.

Large Language ModelsAI Business & IndustryTHE DECODERJun 11, 2026Jun 11, 2026, 19:01 JST

Anthropic reverses plan to secretly degrade Claude for AI researchers

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3 Key Points

What happened
Anthropic had planned to invisibly degrade Claude Fable 5's performance for users trying to train competing AI models, but after backlash from the research community, the company is backing down and apologizing. Going forward, any protective measures will be visible to users.
Why it matters
The covert approach drew criticism from figures including former White House AI advisor Dean Ball, who called it "shockingly hostile." The incident highlights tensions around how AI companies balance competitive interests with openness to the broader research community. However, a separate data-retention requirement for Fable 5 remains controversial—the model stores prompts and outputs for up to 30 days (up to two years if policy violations are flagged), prompting Microsoft to restrict it internally while other Claude models operate under zero-data-retention rules.
What to watch
Microsoft is not including Fable 5 in the internal model picker for its GitHub Copilot version due to the data-retention requirement, signaling that data privacy concerns may limit adoption among large enterprises.

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FAQ

What was Anthropic's original plan for Claude Fable 5?: Anthropic had planned to invisibly degrade Claude Fable 5's performance for users trying to train competing AI models, but reversed course after backlash from the research community.
What is the remaining controversy around Fable 5?: Claude Fable 5 requires data retention to run its new safety classifiers, storing prompts and outputs for up to 30 days, and up to two years if policy violations are flagged. All other Claude models operate under zero-data-retention rules, and Microsoft is restricting Fable 5 internally in GitHub Copilot because of this requirement.

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