Microsoft told employees to steer clear of Anthropic’s Claude Fable 5, just one day after the model launched. The reason: Anthropic now stores user prompts and outputs for 30 days, and Microsoft’s lawyers aren’t comfortable with that.
The restriction, announced on June 10, 2026, applies specifically to Anthropic’s Mythos-class systems, which include the newly released Fable 5.
What changed at Anthropic
Fable 5 launched on June 9, 2026, positioned as a more accessible version of Anthropic’s Mythos 5 model. Alongside the launch, Anthropic updated its data retention policy to require a mandatory 30-day storage window for all prompts and outputs generated through its Mythos-class systems.
Anthropic frames this as a safety measure. The company says the retention window helps it combat emerging threats, including novel attacks and jailbreak attempts targeting its AI systems. The stored data is automatically deleted after 30 days unless it’s flagged for safety investigations or legal purposes. Anthropic has also stated the retained data will not be used for model training.
