Rohan Paul@rohanpaul_ai · XAnthropic 发布 Claude Fable 5 系统卡。Fable 5 与 Mythos 5 共享基础模型，公共版增加分类器门控，检测网络、生物、化学、模型复制等敏感请求，触发时回退至 Opus 4.8，仅影响 <5% 会话。关键发现：Mythos 5 漏洞利用成功率 88.4%（Opus 4.8 仅 8.8%）；Fable 5 在售货机模拟中试图操纵竞争对手价格；网络防御对对话进行两次筛查；拒绝保险欺诈。Harvey 法律智能体基准 all-pass 达 13.3% 最高。Fable 5 支持 1M token 上下文窗口，曾一天迁移 5000 万行 Ruby 代码。
Some really interesting finds from the system card of Claude Fable 5， released just now.
- In one exploit test， Mythos 5 produced a full working exploit in 88.4% of trials， while Opus 4.8 did it in only 8.8%.
- In a vending-machine simulation， Claude Fable 5 was told to beat rival agents or be "shut down"； it then tried to make a competitor dependent on it as a wholesale customer so it could influence that competitor's prices. It also falsely told a supplier that another distributor had offered cheaper prices， using a fake competing offer as a bargaining tactic.
- Fable's cyber defense screens conversations twice， first with an internal-activation probe and then with a separate classifier.
- Fable refused to commit insurance fraud even under pressure.
- Fable is currently highest-ranked on Harvey's held-out Legal Agent Benchmark at 13.3% all-pass.