Microsoft Bars Employees from Claude Fable 5 Over Anthropic Data Retention Rules

Microsoft, despite being one of Anthropic's biggest backers, is quietly restricting internal use of Claude Fable 5. The decision stems from Anthropic's updated data retention requirements, which have raised red flags inside Microsoft over how employee and customer information might be handled. Claude Fable 5 is not available in the model picker used by Microsoft employees for internal GitHub Copilot, while other Claude models remain available internally under Zero Data Retention (ZDR) rules. Claude Fable 5 was unveiled as Anthropic's first "Mythos-class" model and rolled out to GitHub Copilot and Foundry customers almost immediately. Anthropic ties Claude Fable 5 to its safety classifiers so that prompts and outputs are retained for 30 days, and content flagged as violating Anthropic's usage policy can be kept for up to two years. Microsoft has told employees that its legal teams are evaluating Anthropic's retention changes because of concerns about customer data and confidential information.

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