How far ahead of Fable 5 is Anthropic’s internal model by now?

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anthropic fable-5 mythos internal-models ai-progress model-acceleration speculation

Summary

Speculation on how far ahead Anthropic's internal frontier models might be from the publicly released Fable 5 model, given months of feedback and AI-assisted development cycles.

Mythos Preview was already being used by selected organizations in April. It’s now late July, and Anthropic has had several months of feedback, experiments and model-assisted research since then. Fable 5 was released in June, but it was presumably based on a checkpoint developed and tested months earlier. So how far ahead could Anthropic’s best internal model already be? If models at the Mythos/Fable level are actively helping with coding, evaluations and AI research, shouldn’t each development cycle be getting noticeably faster? Maybe the biggest improvements aren’t visible in benchmarks, but in agent reliability, research automation and the number of experiments they can run. I’m not claiming full recursive self-improvement is happening yet. But it feels like we may already be in the early stage where AI is accelerating the development of its successors. Do you think Anthropic’s internal frontier is only slightly ahead of Fable 5, or are they sitting on something significantly more capable?
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