Microsoft Blocks Claude Fable 5 Over Data Retention

What did Microsoft do with Claude Fable 5?

Microsoft has blocked employee access to Claude Fable 5, pulling it from the model picker used in the company's internal version of GitHub Copilot. Other Claude models remain available internally, operating under Zero Data Retention (ZDR) rules. Zero Data Retention means the vendor does not store prompts or outputs after a session ends.

The Verge, as reported by Reuters via MarketScreener, broke the story on June 10, 2026, citing sources familiar with the situation.

What is Claude Fable 5?

Claude Fable 5 is the public release of Anthropic's Mythos AI model — described by Anthropic as the most powerful model it has made available for wider use. Anthropic cited its performance in software engineering and analytics. Anthropic announced the rollout on Tuesday, June 10, with guardrails barring use in risky areas such as cybersecurity.

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Why did Microsoft restrict access?

Anthropic tied Claude Fable 5 to its safety classifiers. Under the new policy, prompts and outputs are retained for 30 days. Content flagged as violating Anthropic's usage policy can be kept for up to two years.

Let's Data Science, summarizing The Verge's reporting, notes those retention windows are the central driver of Microsoft's internal access restrictions. Microsoft has told employees its legal teams are evaluating Anthropic's changes, with concerns focused on customer data and confidential information.

Which Claude models are still available to Microsoft employees?

Other Claude models — those operating under Zero Data Retention rules — remain accessible to Microsoft employees through the internal GitHub Copilot model picker. Only Claude Fable 5 has been removed.

Frequently asked questions

Q: Why did Microsoft restrict Claude Fable 5 for employees? A: Microsoft pulled Claude Fable 5 from its internal GitHub Copilot model picker after Anthropic introduced new data retention rules. Those rules retain prompts and outputs for 30 days and keep flagged content for up to two years. Microsoft's legal teams are evaluating the changes over concerns about customer data and confidential information.

Q: What are Anthropic's data retention rules for Claude Fable 5? A: Under Anthropic's updated policy, prompts and outputs from Claude Fable 5 are retained for 30 days. Content flagged as violating Anthropic's usage policy can be retained for up to two years. These rules are tied to Anthropic's safety classifiers.

Q: What is Zero Data Retention (ZDR)? A: Zero Data Retention means the vendor does not store prompts or outputs after a session ends. Other Claude models available to Microsoft employees internally operate under ZDR rules, which is why they were not affected by this restriction.

Q: What is Claude Fable 5? A: Claude Fable 5 is the public release of Anthropic's Mythos AI model. Anthropic describes it as the most powerful model it has made available for wider use, highlighting its performance in software engineering and analytics. Anthropic announced the rollout on June 10, 2026, with guardrails against use in risky areas such as cybersecurity.

Q: Are Microsoft's legal teams still reviewing Anthropic's retention policy? A: Yes. As of June 10, 2026, Microsoft has told employees that its legal teams are actively evaluating Anthropic's data retention changes. No resolution or contractual update has been reported.