--- title: Claude Fable 5 and Claude Mythos 5 | daily.dev description: Anthropic has released Claude Fable 5, built on the same weights as the restricted Mythos model but with built-in safety classifiers that reroute high-risk... canonical: https://daily.dev/posts/claude-fable-5-and-claude-mythos-5-t3o5ecdo5 twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Claude Fable 5 and Claude Mythos 5 | daily.dev og:description: Anthropic has released Claude Fable 5, built on the same weights as the restricted Mythos model but with built-in safety classifiers that reroute high-risk... og:url: https://daily.dev/posts/claude-fable-5-and-claude-mythos-5-t3o5ecdo5 og:image: https://api.daily.dev/og/posts/t3o5EcDo5.png og:image:alt: Claude Fable 5 and Claude Mythos 5 og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Claude Fable 5 and Claude Mythos 5 **[Md. Shafin Ahmed](https://daily.dev/sources/u8ir8dacsyjsphydqqtq9)** · [@mdshafinahmed](https://daily.dev/mdshafinahmed) · 2 min read · 3 upvotes · 2 comments ## Summary Anthropic has released Claude Fable 5, built on the same weights as the restricted Mythos model but with built-in safety classifiers that reroute high-risk queries to Claude Opus 4.8 (affecting under 5% of sessions). Benchmark highlights include 80.3% on SWE-Bench Pro vs GPT-5.5's 58.6%, and 29.3% on FrontierCode Diamond vs 5.7%. Real-world use cases include Stripe migrating a 50-million-line Ruby codebase in a single day. The restricted Mythos 5 autonomously ran genomics research, trained a custom ML model across 138 species, and outperformed a published Science paper model while being 100× smaller. Pricing is $10/1M input and $50/1M output, free on Pro/Max/Team plans until June 22. A new 30-day data retention policy now applies to all users including enterprise customers with prior zero-retention agreements. ## Content Anthropic just released Claude Fable 5 — their most powerful model ever made publicly available. Here's what you need to know: 🔬 What it is: Fable 5 runs on the same underlying weights as Mythos — the model that shocked the cybersecurity world in April. The difference? Built-in safety classifiers that reroute high-risk queries (cyber, biology, chemistry) to Claude Opus 4.8 automatically. Less than 5% of sessions are affected. 📊 Benchmark highlights (vs GPT-5.5): → SWE-Bench Pro: 80.3% vs 58.6% → FrontierCode Diamond: 29.3% vs 5.7% → CursorBench: 72.9% — 8pts above previous best → Frontier physics research: matched 4 days of GPT-5.5 work in 36 hours, using ⅓ the reasoning tokens 🏗️ Real-world proof: Stripe used it to migrate a 50-million-line Ruby codebase in a single day — a job that would take a full engineering team over two months. 🧬 The science angle is underrated: Mythos 5 (the restricted version for vetted partners) autonomously ran genomics research over a week, trained a custom ML model across 138 animal species, and outperformed a recently published model in Science — while being 100× smaller. ⚠️ Two things worth knowing before you deploy: 1. Safety filters are deliberately broad — some benign security tasks may get rerouted 2. New 30-day data retention policy applies to ALL users, including enterprise customers with previous zero-retention agreements (not for training, but for safety monitoring) 💰 Pricing: $10/1M input · $50/1M output Free on Pro/Max/Team plans until June 22, then usage credits required. This isn't just a faster model. It's the first AI that genuinely improves the longer it runs — designed for hours or days of autonomous work, not just single exchanges. The capability bar just moved. Is your team ready to use it — and use it responsibly? 🔗 Full announcement: anthropic.com/news/claude-fable-5-mythos-5 #AI #Anthropic #ClaudeFable5 #LLM #SoftwareEngineering #AISafety #TechNews #FutureOfWork #MachineLearning ## Community discussion Top comments from developers on daily.dev. **@mdshafinahmed** · 1 upvotes > I think this will be most out breaking model of Claude AI. --- Tags: [#llm](https://daily.dev/tags/llm), [#anthropic](https://daily.dev/tags/anthropic), [#ai-coding](https://daily.dev/tags/ai-coding), [#ai-safety](https://daily.dev/tags/ai-safety) [View this post on daily.dev](https://daily.dev/posts/claude-fable-5-and-claude-mythos-5-t3o5ecdo5) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"DiscussionForumPosting","mainEntityOfPage":"https://daily.dev/posts/claude-fable-5-and-claude-mythos-5-t3o5ecdo5","headline":"Claude Fable 5 and Claude Mythos 5","text":"Anthropic has released Claude Fable 5, built on the same weights as the restricted Mythos model but with built-in safety classifiers that reroute high-risk queries to Claude Opus 4.8 (affecting under 5% of sessions). 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