Microsoft has blocked its own employees from using Anthropic’s Claude Fable 5, the AI company’s newest and most capable model, while its legal team reviews data retention policies that could keep sensitive corporate prompts stored for up to two years.
The restriction, reported on June 10, 2026, creates an awkward split: external Microsoft customers can access Fable 5 through GitHub Copilot and Microsoft Foundry, but the people who actually built those platforms cannot touch the model internally.
The retention problem
Previous versions of Anthropic’s Claude models were available to Microsoft with zero-data-retention configurations, commonly known as ZDR. That meant prompts typed by Microsoft employees and the outputs they received were not stored by Anthropic.
Claude Fable 5, which launched on June 9, 2026, as part of Anthropic’s Mythos-class lineup, changes that calculus entirely. The model mandates a minimum data retention period of 30 days for all prompts and outputs.
