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

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) Why They Really Really Shouldn't Have Done That In That Way(12:02) They Get Letters(16:11) What's In A Name(18:13) Executive Summary Of Their Executive Summary(19:28) Introduction (1)(19:55) RSP Evaluations (2.1 and 2.2)(23:01) AI Research And Development (2.3)(25:48) Alignment Risk (2.4)(27:21) Cyber (3)(30:30) Jailbreak Robustness(32:04) Yay UK AISI(32:32) Mundane Safety (4)(34:26) Agentic Safety (5)(36:19) Alignment (6)(42:25) In Vendbench(45:19) White Box Investigations (6.4)(47:53) Grading Awareness(51:20) Guess The Teacher's Password(52:33) It Knows This Is A Test And This Is Fine(56:03) I'm The Real Shady(58:06) The Lighter Side --- First published: June 12th, 2026 Source: https://www.lesswrong.com/posts/ixJDkQBncJBshcvwj/claude-fable-5-and-mythos-5-the-system-card --- Narrated by TYPE III AUDIO. ---Images from the article:Apple Podcasts and Spotify do not show images in the episode description. Try Pocket Casts, or another podcast app.