Microsoft warns employees: Do not use Anthropic’s Claude Fable, our lawyers are…

Anthropic launched Claude Fable 5 on Tuesday, its first Mythos-class model and the most powerful one the company has cleared for wider use. Within a day, Microsoft had quietly walked it out of the building. The Verge reports that Microsoft is restricting employee access to Fable 5 over Anthropic’s new data retention requirements, even as it rolled the same model out to its GitHub Copilot and Foundry customers without missing a beat. Every other Claude model is still available to staff, because they run under Zero Data Retention. Fable 5 does not, and that single technical difference has Microsoft’s legal team holding the line.

The split treatment is unusual, especially given how deeply the two companies are now wired together, from the November Foundry deal covering Sonnet 4.5, Opus 4.1, and Haiku 4.5 to the Claude tech now sitting inside Microsoft 365 Copilot.