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Anthropic releases Fable 5.1 and restricted Mythos 5.1
Tracks the paired model release, access distinctions, benchmark results and enterprise inference economics.
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Overview
Anthropic released broadly available Fable 5.1 alongside restricted Mythos 5.1, described as sharing underlying intelligence with different safety envelopes. Moonshots highlighted strong expert-reasoning results and 75 percent cheaper cache reads, arguing that reusable business context improves enterprise economics and responsiveness. Box founder Aaron Levie later said that on Box's document-centric Complex Work Eval and internal holdback tests, model quality mostly tracks coding leaderboards, with Gemini stronger than its coding reputation on some knowledge-work tasks, and that Fable 5.1 was clearly the best model Box had seen, in a tight race with Grok, Muse, the Fable class, and GPT-5.6.
Recent coverage
Changes to our coverage published in the past seven days. These are site update dates; podcast discussion dates and sources are in each version.
No changes to this account were published in the past seven days.
What changed
Dates show when each podcast discussion was published.
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New information
Aaron Levie said Box's enterprise document evals found Fable 5.1 clearly state of the art for Box's use case. He said overall model ranking still closely follows coding performance, except that Gemini is disproportionately strong on some knowledge-work tasks, and that Grok, Muse, the Fable class, and GPT-5.6 remain in a tight race.
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New information
The panel presents Fable 5.1 as a leading general-purpose model and connects cheaper cached context to faster, more practical enterprise workflows.
Podcast discussions
- Training Data Box's Aaron Levie: On Reinventing Yourself in the AI Age and Enterprise DiffusionSep 15, 2026
- Moonshots with Peter Diamandis GPT-6 Astra Saturates ARC-AGI-3, Tesla's $30K Cybercab Floods Austin, Anthropic Proves Fermat's Last Theorem | EP #286Sep 5, 2026
Sources
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Our coverage
Anthropic's cached-read cut makes business context the prize: panelist
Anthropic's Fable 5.1 cuts cached reads to $0.25 per million tokens, a quarter of Fable 5's rate. A Moonshots panelist said this makes a company's reused context the prize, as model leads last only about a month.
Version history
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Sep 16, 2026 · Version 2
Aaron Levie said Box's enterprise document evals found Fable 5.1 clearly state of the art for Box's use case. He said overall model ranking still closely follows coding performance, except that Gemini is disproportionately strong on some knowledge-work tasks, and that Grok, Muse, the Fable class, and GPT-5.6 remain in a tight race.