Anthropic has released Claude Fable 5.1 and its restricted sibling Mythos 5.1, the company's first major model update since export controls forced it to pull Fable 5 offline for 18 days three months ago. The new model more than doubles its predecessor's performance on a key benchmark.
The New Models
Fable 5.1 is the latest iteration of Anthropic's flagship Claude line. The company says it more than doubles the score of the previous version on a key benchmark, though it hasn't specified which one. Mythos 5.1 is a restricted version of Fable 5.1, designed for users who need tighter guardrails or compliance with certain regulations.
Both models are available now, but Anthropic hasn't detailed the exact restrictions on Mythos 5.1. The company also hasn't said which users or regions get access to which version.
Why Fable 5 Went Dark
Three months ago, export controls forced Anthropic to pull Fable 5 offline for 18 days. The move came after regulators tightened rules on advanced AI models, and Anthropic had to comply or face penalties. The outage was a rare disruption for a company that typically ships updates on a regular cadence.
The 18-day gap left many users without access to the model. Anthropic didn't explain the specifics of the export controls at the time, but the company has now resumed shipping with Fable 5.1.
What Mythos 5.1 Means
Mythos 5.1 is a restricted version of Fable 5.1. That means it likely has reduced capabilities or additional safety measures, but Anthropic hasn't spelled out what's different. The company has only said it's a restricted version, leaving developers and enterprise customers to guess at the limitations.
This isn't the first time Anthropic has offered a restricted model. But the timing here is notable: the release comes just three months after the export control incident, suggesting the company is trying to balance innovation with regulatory pressure.
Anthropic hasn't said when it will provide more details on Mythos 5.1's restrictions, or whether Fable 5.1 will eventually be available to all users without conditions. For now, the company is moving forward with a two-tier approach.
