Anthropic releases new Mythos and Fable models amid RSI concerns

Anthropic released new versions of its most advanced models on Monday, with the launch of Mythos 5.2 and Fable 5.2. The company says the new models “show improvements in areas like coding, reasoning, and vision,” and communicate more clearly with users.

Notably, Anthropic is lowering the cost of Fable from $10 to $8 per million input tokens. As a result, Fable 5.2 is now cheaper than its primary competitor GPT-6 Astra. Anthropic says that the new version of Fable will return responses 30% faster across effort levels. Faster inference serving is available for double the price.

Fable 5.2 is also compatible with zero data retention (ZDR) policies through the Enterprise Frontier Safeguards system, long a sticking point for many enterprise clients.

It’s Anthropic’s first model release since the arrival of a third-party report from the assessment group METR, which suggested the lab might be approaching recursive self-improvement (RSI) — or the ability for AI models to carry on model training independently. The METR report found internal models were speeding up Anthropic’s AI progress by roughly 2x, although many uncertainties remain.

Still, Anthropic’s release notes significant ongoing challenges in accurately testing model capabilities. “Claude Mythos 5.2 and Fable 5.2 each voice suspicion that they are being evaluated more often than any of our recent models, which challenges our ability to assess how they will act in real-world settings. As these settings expand and capabilities increase with future models, we expect this challenge to grow.”