September 28, 2026
Open models have yet to make the leap to agents: Mollick highlights Fable and Astra
On Sep 27, Ethan Mollick called the gap between open and closed models the largest in a long time. He placed Claude Fable 5.1 and GPT-6 Astra in a class of models that can operate as AI agents in ways models before Fable could not.
Ethan Mollick
@emollick
The gap between open and closed models is now noticeably larger than it has been in a long time. Models in the Fable and Astra class can operate as agents in ways models before Fable could not, for better or worse. No open model has crossed that threshold yet. When one does, it will be a leap.
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Mollick writes that open models have not yet crossed the threshold at which a model can act as an agent. For practical work, the choices diverge: teams run Claude Code with Fable 5.1 in the terminal, while GPT-6 Astra is called through the Responses API.
The pricing matches. Fable 5.1 and Astra offer a 1 million-token window and cost $10 per 1 million input tokens and $50 per 1 million output tokens. Cache reads for Fable 5.1 cost $0.25 per 1 million tokens.
The next milestone will be an open model that, in Mollick's words, crosses that threshold.
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