Anthropic unveils Claude Fable 5.1 and Mythos 5.1 with lower costs and watermarks
Anthropic introduced Claude Fable 5.1, generally available, and Mythos 5.1, for trusted partners with additional safeguards in cybersecurity and life sciences. Fable 5.1 claims stronger coding and science performance, with overall costs estimated 25% lower for typical workloads and up to 45% lower for agentic tasks, partly via 75% cheaper cache reads. These are Anthropic's first models to watermark text outputs, with a detection API for eligible groups per EU law.
Coverage timeline
Hacker Newsmeetpateltech
Techmeme
Anthropic : Anthropic unveils Claude Fable 5.1, which is generally available, and Mythos 5.1, for trusted partners and with cybersecurity and life sciences safeguards — We're introducing Claude Fable 5.1 and Claude Mythos 5.1. They're the world's most advanced models for coding and knowledge work …
Rachel Metz / Bloomberg : Anthropic says Fable 5.1 will cost an estimated 25% less than Fable 5 for typical workloads and up to 45% less for highly agentic work — Anthropic PBC is releasing a new version of its powerful Fable artificial intelligence model that it says is better at coding and science tasks …
Carl Franzen / VentureBeat : Anthropic says Fable 5.1 sets new standards on coding, knowledge work, and long-running problem-solving tasks, and can fix the root causes of software issues — It's only the first day of September 2026, but the month and fall season are already off to the races in AI land …
TechCrunch AIRussell Brandom
Fable 5.1 includes changes meant to reduce token cost and false-positive restrictions from the model's safeguards.
Ben Patterson / PCWorld : Claude Fable 5.1 and Mythos 5.1 are Anthropic's first models to watermark text outputs; a detection API is available to eligible groups as required under EU law — Aside from being more powerful than their predecessors, Claude Fable 5.1 and Mythos 5.1 will add invisible watermarks all their text and file outputs.
The Verge AIStevie Bonifield
Anthropic says its newest AI models, Fable 5.1 and Mythos 5.1 , address criticisms from customers about price, data retention, and overzealous safeguards. The company claims Claude Fable 5.1 offers stronger performance than Fable 5, but costs around 25 percent less typically and up to 45 percent less for complex agentic tasks, thanks to reduced pricing on cached data that was already processed and stored. Along with the announcement, a slew of early impressions popped up, including from Every CEO Dan Shipper, who claims , "It's the strongest coding model we've used, but now it's fast, token-efficient, and crucially actually speaks like a norm … Read the full story at The Verge.
Frederic Lardinois / The New Stack : Anthropic prices Fable 5.1 at $10/1M input tokens and $50/1M output tokens, unchanged from Fable 5, and cuts cache read pricing by 75% to $0.25/1M tokens — Anthropic keeps Fable's $10/$50 pricing, cuts cache reads by 75%, and tunes the safeguards that made Fable 5 punt to Opus.
Zac Hall / 9to5Mac : Anthropic says Fable 5.1 will cost an estimated 25% less than Fable 5 for typical workloads and up to 45% less for highly agentic work — In June, Anthropic first released Fable 5, its Mythos-class AI model for Claude. Three months later, Anthropic is enhancing Claude with its new Fable 5.1 model upgrade.
Simon Willison
Today is Claude Fable (and Mythos) 5.1 day . Anthropic say that Fable 5.1 "sets a new standard for coding, knowledge work, and long-running problem-solving tasks". Their announcement spends a notable amount of time on scientific research, boasting of a 52.6% score on the brand new Terminal-Bench-Science 0.1 benchmark (first announced on August 27th ), up from 24.7% for Fable 5, 29.0% for Opus 5 and 22.4% for GPT-5.6 Sol. Other benchmarks show slightly improved scores, but none as impressive as the Science one. But how well can it pelican? Back in July I wrote about how I was losing faith in the pelican benchmark - its connection to how good the models were at other tasks didn't seem to hold as strongly as it did back in 2025 . The most interesting insights I get from it now are comparisons within model families, and particularly comparisons for the same prompt at different reasoning effort levels. Fable 5.1 has five reasoning levels: low, medium, high, xhigh, max - and no option to tur
机器之心机器之心
就在刚刚， Anthropic 推出新一代模型 Claude Fable 5.1 和 Claude Mythos 5.1 。 Anthropic 称 Claude Fable 5.1 是目前最强大的公开可用模型之一 ，专为复杂推理、长周期任务和 Agent 工作流打造。而 Claude Mythos 5.1 则代表他们探索的更高能力边界。 需要注意的是， 虽然两者共享相同的基础模型能力，但针对不同使用场景采用了不同的安全措施 。 其中 Fable 5.1 面向普通用户、开发者和企业开放，Mythos 5.1 则面向经过审核的高风险领域合作伙伴，保持更严格访问控制。 换句话说，一个负责进入现实世界工作，另一个则被留在更严格控制的环境里。而这也或许是 Anthropic 对未来 AI 产品形态的一次探索： 最强模型，不一定会以同一种形式提供给所有人。 官方则表示，这两个模型代表了 Claude 系列能力的重要进展，并展示了他们如何在提升模型能力的同时，继续推进安全部署。 作为「地表最强」模型的 Fable 5.1，性能表现依旧能打，官方数据显示，Fable 5.1 多项基准测试的表现均优于上一代旗舰 Fable 5。 但能力更强，价格却便宜了 。Anthropic 表示，Fable 5.1 保持基础价格不变，缓存读取成本相比 Fable 5 降低了 75%。在实际使用中，这使模型的整体成本对于典型工作负载降低约 25%；对于高度 Agent 化的工作负载，成本最高可降低 45%。 看来，就连最强大模型也在讲究性价比了。 下面来具体看一下。 低档位追平上一代，Fable 5.1 主打「性价比」 相比单纯刷新榜单，Anthropic 这次更想强调的是： Fable 5.1 可以用更低的推理成本，完成过去需要 Fable 5 高档位才能完成的任务。 根据官方测试，Fable 5.1 在低、中等推理强度下，已经能够取得接近甚至超过 Fable 5 的表现。Claude Code 默认使用高推理强度，Claude Cowork 和 Claude.ai 则默认使用中等强度，用户也可以根据任务复杂程度，在速度、成本与效果之间进行调整。 具体来看，Fable 5.1 在科学研究型 Agent 基准 Terminal-Bench-Science 0.1 中取得 52.6% 的成绩，相比
