Microsoft has blocked its own employees from using Anthropic's newly launched Claude Fable 5 inside GitHub Copilot, citing unresolved concerns over a 30-day data retention policy tied to the Mythos-class model. The Verge reports Microsoft's legal team is still reviewing the changes, even as paying Copilot and Foundry customers already have access. Other Claude models remain available internally under Zero Data Retention rules. Anthropic has not offered a workaround.