--- title: Anthropic’s Fable 5.1 is a bit cheaper, a bit smarter,... description: Anthropic released Fable 5.1 and Mythos 5.1, keeping the $10/$50 per million token pricing but cutting cache read costs by 75% to $0.25 per million. The model... canonical: https://daily.dev/posts/anthropic-s-fable-5-1-is-a-bit-cheaper-a-bit-smarter-and-refuses-a-lot-less-ln0xgxsnc twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Anthropic’s Fable 5.1 is a bit cheaper, a bit smarter, and refuses a lot less | daily.dev og:description: Anthropic released Fable 5.1 and Mythos 5.1, keeping the $10/$50 per million token pricing but cutting cache read costs by 75% to $0.25 per million. The model... og:url: https://daily.dev/posts/anthropic-s-fable-5-1-is-a-bit-cheaper-a-bit-smarter-and-refuses-a-lot-less-ln0xgxsnc og:image: https://api.daily.dev/og/posts/ln0XgxSnc.png og:image:alt: Anthropic’s Fable 5.1 is a bit cheaper, a bit smarter, and refuses a lot less 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. # Anthropic’s Fable 5.1 is a bit cheaper, a bit smarter, and refuses a lot less **[The New Stack](https://daily.dev/sources/newstack)** · 6 min read · 0 upvotes · 0 comments ## Summary Anthropic released Fable 5.1 and Mythos 5.1, keeping the $10/$50 per million token pricing but cutting cache read costs by 75% to $0.25 per million. The model outperforms Fable 5 and Opus 5 on most benchmarks, with a major jump on the Terminal-Bench-Science 0.1 agentic science benchmark (52.6% vs 24.7%). Claude Code safeguards now intervene about 60% less on cyber requests and 85% less on biology/medical queries, and the model can now flag code vulnerabilities though penetration testing and exploit generation still redirect to Opus. Anthropic also opened a watermark detection API in private preview for EU-mandated organizations, introduced Enterprise Frontier Safeguards to offer zero-data-retention-equivalent privacy by storing monitoring data in customer-controlled cloud storage, and added anti-distillation restrictions to the API that block editing Claude's prior context while preserving its thinking transcript. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### What changed in pricing between Claude Fable 5 and Fable 5.1? Input and output token pricing stays the same at $10 and $50 per million tokens, but cache read pricing drops 75% to $0.25 per million tokens. Fable 5.1 is generally available while Mythos 5.1 remains restricted to Anthropic's trusted access program due to added cybersecurity and life-sciences safeguards. _Track pricing shifts like this on daily.dev before budgeting your next API integration._ ### Why did Claude Fable 5 defer so often to Opus models in Claude Code? Fable 5's safeguards were overly cautious and would hand off to Opus whenever it detected the user might be pushing against safety limits, even for benign requests like medical questions or vulnerability scanning for defensive purposes. Fable 5.1 tunes these safeguards to intervene about 60% less on cyber-related sessions and 85% less on biology and medical questions, while still blocking penetration testing, exploit generation, and binary vulnerability scanning. _Developers relying on Claude Code for security work follow safeguard tuning like this on daily.dev._ ### How does Anthropic's Enterprise Frontier Safeguards system provide zero data retention while still monitoring for misuse? Enterprise Frontier Safeguards (EFS) stores conversation data in cloud infrastructure controlled entirely by the customer, such as Amazon S3, Azure Blob Storage, or Google Cloud Storage, encrypted with the customer's own keys. Anthropic then runs automated misuse detection against that data with no human review on its side, routing alerts back to the customer, rolling out in phases starting later in the fall at no extra cost beyond storage fees. _Enterprise teams weighing data retention trade-offs track policy changes like this on daily.dev._ --- Tags: [#llm](https://daily.dev/tags/llm), [#claude](https://daily.dev/tags/claude), [#anthropic](https://daily.dev/tags/anthropic), [#claude-code](https://daily.dev/tags/claude-code), [#ai-safety](https://daily.dev/tags/ai-safety) [View this post on daily.dev](https://daily.dev/posts/anthropic-s-fable-5-1-is-a-bit-cheaper-a-bit-smarter-and-refuses-a-lot-less-ln0xgxsnc) ```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":"TechArticle","headline":"Anthropic’s Fable 5.1 is a bit cheaper, a bit smarter, and refuses a lot less","url":"https://daily.dev/posts/anthropic-s-fable-5-1-is-a-bit-cheaper-a-bit-smarter-and-refuses-a-lot-less-ln0xgxsnc","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/anthropic-s-fable-5-1-is-a-bit-cheaper-a-bit-smarter-and-refuses-a-lot-less-ln0xgxsnc"},"datePublished":"2026-09-01T19:41:59.789Z","dateModified":"2026-09-01T20:08:00.719Z","description":"Anthropic released Fable 5.1 and Mythos 5.1, keeping the $10/$50 per million token pricing but cutting cache read costs by 75% to $0.25 per million. 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Fable 5.1 is generally available while Mythos 5.1 remains restricted to Anthropic's trusted access program due to added cybersecurity and life-sciences safeguards. Track pricing shifts like this on daily.dev before budgeting your next API integration."}},{"@type":"Question","name":"Why did Claude Fable 5 defer so often to Opus models in Claude Code?","acceptedAnswer":{"@type":"Answer","text":"Fable 5's safeguards were overly cautious and would hand off to Opus whenever it detected the user might be pushing against safety limits, even for benign requests like medical questions or vulnerability scanning for defensive purposes. Fable 5.1 tunes these safeguards to intervene about 60% less on cyber-related sessions and 85% less on biology and medical questions, while still blocking penetration testing, exploit generation, and binary vulnerability scanning. 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