“Claude Fable 5 and Mythos 5: Capabilities” by Zvi

Only three days after the release of Claude Fable 5, Anthropic was forced by the United States Government to make it unavailable, when a jailbreak was brought to its attention, rather than the previous situation of ‘yes obviously experts can jailbreak anything if they care enough’ and ‘yes obviously you can ask Fable to fix your code.’ Three days was enough time for many of us to learn to love Fable, and for us to dearly miss it now that it is gone. The world was briefly smarter, and now it is again stupider. At some point it will get smarter again, which will likely be within two weeks. This post is written as if Fable 5 is again available for public use, rather than trying to include a lot of qualifying clauses. It remains to be seen how this will play out, and this post does not attempt to cover that question. My previous release coverage of Fable covered the model card and then model welfare. Coverage of the government takedown of Fable starts here, and continues here and here. The Official Pitch The pitch is that Fable 5 is the best model [...] ---Outline:(01:08) The Official Pitch(04:06) Technical Details(04:31) The System Prompt and Jailbreak(06:45) Benchmarks(15:22) Other People's Benchmarks(21:08) The Classifiers Are Not Messing Around(22:53) The Classifiers Need Work(28:15) The Classifiers Have Consequences(29:18) First Hit Is Free(29:53) How Easily We Forget(30:46) Data Retention Is An Issue(31:15) Fable For The Win(36:15) Andrej Karpathy Is Impressed(37:54) Every Is Very Impressed(39:04) Other People Are Impressed(51:10) Know How To Tell a Fable(53:06) You Can Just Make Things(55:37) You Can Just Install Things(56:05) Good Personality(57:51) Fable Writes A Fable(01:06:04) Is That Code(01:08:32) Fable Crosses The Threshold(01:09:12) Man With A Plan(01:10:12) Less Impressed Assessments(01:13:39) Actively Negative Assessments(01:14:16) Coherence(01:15:27) Good Night And Good Luck(01:16:05) Curious Fable(01:16:23) I See You, Baby(01:16:40) We Finally Did It We Know How To Count Letters(01:17:46) That's Not My Style(01:20:12) The Lighter Side --- First published: June 19th, 2026 Source: https://www.lesswrong.com/posts/kMnobCQp9z2pSbzDB/claude-fable-5-and-mythos-5-capabilities --- 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.