--- title: Anthropic releases Claude Fable 5.1 and Mythos 5.1,... description: Anthropic released Claude Fable 5.1 and Mythos 5.1, described as the same underlying model with different safeguards. Fable is generally available while Mythos... canonical: https://daily.dev/posts/anthropic-releases-claude-fable-5-1-and-mythos-5-1-cutting-cache-read-prices-by-75--k5k9jf7ng twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Anthropic releases Claude Fable 5.1 and Mythos 5.1, cutting cache read prices by 75% | daily.dev og:description: Anthropic released Claude Fable 5.1 and Mythos 5.1, described as the same underlying model with different safeguards. Fable is generally available while Mythos... og:url: https://daily.dev/posts/anthropic-releases-claude-fable-5-1-and-mythos-5-1-cutting-cache-read-prices-by-75--k5k9jf7ng og:image: https://api.daily.dev/og/posts/K5K9jf7ng.png og:image:alt: Anthropic releases Claude Fable 5.1 and Mythos 5.1, cutting cache read prices by 75% 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 releases Claude Fable 5.1 and Mythos 5.1, cutting cache read prices by 75% **[The Next Web](https://daily.dev/sources/tnw)** · 3 min read · 0 upvotes · 0 comments ## Summary Anthropic released Claude Fable 5.1 and Mythos 5.1, described as the same underlying model with different safeguards. Fable is generally available while Mythos is restricted to vetted cybersecurity and life-sciences users through programmes built with the US government. Cache read prices drop 75% to $0.25 per million tokens, cutting typical workload costs by about 25% and agentic workload costs by up to 45%. Fable 5.1 scores 52.6% on Terminal-Bench-Science 0.1, up from 24.7% for Fable 5, and 55.8% on Terminal-Bench 4.0. Outputs now carry an invisible watermark required by the EU AI Act's Article 50, applicable to models released after August 2, 2026. A promised free detection API has instead shipped as a narrower private preview limited to regulators, law enforcement, media, fact-checkers, researchers, and EU civil society groups, with no date given for wider access. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### How much cheaper are cache reads with Claude Fable 5.1 compared to previous models? Cache read prices for Claude Fable 5.1 fall 75% to $0.25 per million tokens. Anthropic says this cuts typical workload costs by about 25% and agentic workload costs by up to 45%, making cached context substantially cheaper to use in production applications. _Developers tracking API pricing shifts can follow Claude cost changes like this on daily.dev._ ### What is the EU AI Act watermark requirement for Claude models released after August 2026? Under Article 50 of the EU AI Act, providers must mark synthetic AI output in a machine-readable, detectable format, a duty that has applied since August 2, 2026. Claude models released after that date carry an invisible watermark containing no information about the user, verifiable only through Anthropic's detection tool. _Teams navigating AI Act compliance can keep up with watermarking and detection changes on daily.dev._ ### Is Anthropic's Claude watermark detection API publicly available? No, the detection API is in private preview rather than the free, open tool Anthropic previously said it would ship. Access is limited to eligible organizations such as regulators, law enforcement, media, fact-checkers, independent researchers, educational bodies, and EU civil society groups, with enterprises able to apply but no timeline given for broader access. _Follow how AI compliance tooling access evolves for developers building on daily.dev._ --- Tags: [#llm](https://daily.dev/tags/llm), [#claude](https://daily.dev/tags/claude), [#anthropic](https://daily.dev/tags/anthropic), [#ai-regulation](https://daily.dev/tags/ai-regulation) [View this post on daily.dev](https://daily.dev/posts/anthropic-releases-claude-fable-5-1-and-mythos-5-1-cutting-cache-read-prices-by-75--k5k9jf7ng) ```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 releases Claude Fable 5.1 and Mythos 5.1, cutting cache read prices by 75%","url":"https://daily.dev/posts/anthropic-releases-claude-fable-5-1-and-mythos-5-1-cutting-cache-read-prices-by-75--k5k9jf7ng","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/anthropic-releases-claude-fable-5-1-and-mythos-5-1-cutting-cache-read-prices-by-75--k5k9jf7ng"},"datePublished":"2026-09-01T20:20:58.033Z","dateModified":"2026-09-01T20:46:41.914Z","description":"Anthropic released Claude Fable 5.1 and Mythos 5.1, described as the same underlying model with different safeguards. 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Anthropic says this cuts typical workload costs by about 25% and agentic workload costs by up to 45%, making cached context substantially cheaper to use in production applications. Developers tracking API pricing shifts can follow Claude cost changes like this on daily.dev."}},{"@type":"Question","name":"What is the EU AI Act watermark requirement for Claude models released after August 2026?","acceptedAnswer":{"@type":"Answer","text":"Under Article 50 of the EU AI Act, providers must mark synthetic AI output in a machine-readable, detectable format, a duty that has applied since August 2, 2026. Claude models released after that date carry an invisible watermark containing no information about the user, verifiable only through Anthropic's detection tool. 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