“Claude Fable 5 and Mythos 5: The System Card” by Zvi

“Claude Fable 5 and Mythos 5: The System Card” by Zvi

From LessWrong (30+ Karma) by LessWrong

June 12, 2026 · 60 min

About this episode

Zvi discusses the capabilities and limitations of the new AI model Claude Fable 5 compared to previous models.

First things first: Claude Fable 5 is the new best publicly available model. I have noticed a step change, where Fable can suddenly help me in ways that previous models were not worth bothering to query. Almost everything it has noticed in one of my drafts so far has been spot on and it is downright scary. Suddenly I am motivated to once again continue improving my Chrome extension. I only ask for things I actually want or am curious about, and it has nailed every question I have asked it. That does not mean it is the right tool for every job. There are four good reasons to often not use Fable. Speed and price. Fable is importantly slower and more expensive than Opus 4.8, and often you will not need to make this trade. After the 22nd, when Fable may no longer be included in subscription plans if demand is too high, we may have to all pay by the token outside our subscriptions (although I suspect subscribers will get at least some credits to help with this), which could add up fast. Relative strengths. Capabilities are jagged. There will still [...] --- Outline: (02:05) Another Week Another Giant System Card (03:02) How To Tell A Fable (08:33) Why They Did That In That Way (10:14)…

People in this episode

Host: Zvi

Topics covered

  • AI models
  • technology
  • product evaluation
  • Chrome extension
  • alignment risk

Keywords

  • Claude Fable 5
  • Opus 4.8
  • AI research
  • Chrome extension
  • alignment risk

Mentioned in this episode

Products: Claude Fable 5, Opus 4.8

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