Rohan Paul@rohanpaul_ai · XAnthropic 推出 Claude Fable 5，一个面向公众的 Mythos 级大语言模型。Fable 5 与 Mythos 5 共享同一基础模型，但增加了分类器门控，检测到敏感的网络、生物、化学及模型复制请求时，将请求回退至 Opus 4.8（而非直接拒绝）。该模型具备长程自主能力：一天内完成 5000 万行 Ruby 代码迁移、截图转代码，并拥有 100 万 token 上下文窗口。Anthropic 称回退仅由窄域主题触发，平均出现在不到 5% 的会话中。模型能力超过此前所有公开发布的版本。
Anthropic finally released Claude Fable 5， a public Mythos-class model.
Fable 5 and Mythos 5 share one underlying model， but Fable adds classifier gates for everyone while Mythos lifts some gates for vetted cyber and infrastructure partners.
i.e. the public version is wrapped in classifier gates that detect sensitive cyber， biology， chemistry， and model-copying requests.
When those gates trigger， the user does not get a normal refusal； the request is handed to Opus 4.8， which means Anthropic is using model fallback as a control system.
Anthropic says the leap is longer-range autonomy： a 50M-line Ruby migration in 1 day， screenshot-to-code work， has a 1M-token context window，
That is the crucial shift： the product is no longer just a model， but a routing machine that decides which level of intelligence a user is allowed to touch for each request.
The limit is that this routing is not arbitrary and not for every subject； Anthropic says the fallback is triggered by a narrow set of topics and appears in less than 5% of sessions on average.