Anthropic released Fable and Mythos 5.1
Anthropic released Claude Fable 5.1 for general use and Claude Mythos 5.1 through trusted-access programs. The company says both versions use the same underlying model with different safeguard levels. Anthropic estimates that Fable 5.1 will cost 25 percent less than Fable 5 on typical token-billed work. It estimates savings up to about 45 percent on highly agentic work because cache-read prices are lower. Anthropic also says its new cyber safeguards produce 60 percent fewer false positives. Enterprise Frontier Safeguards are scheduled to roll out in phases later this fall. Anthropic says they keep monitored data in customer-controlled infrastructure.
Verified 2:43 AM PDT · 2 original sources
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What happened
Anthropic released Claude Fable 5.1 for general use and Claude Mythos 5.1 through trusted-access programs. The company says both versions use the same underlying model with different safeguard levels. Anthropic estimates that Fable 5.1 will cost 25 percent less than Fable 5 on typical token-billed work. It estimates savings up to about 45 percent on highly agentic work because cache-read prices are lower. Anthropic also says its new cyber safeguards produce 60 percent fewer false positives. Enterprise Frontier Safeguards are scheduled to roll out in phases later this fall. Anthropic says they keep monitored data in customer-controlled infrastructure.
Pressure point
The price, performance, and safeguard figures come from Anthropic, not independent tests. TechCrunch reported that Anthropic's system card calls Mythos 5.1 a slight regression from Opus 5 on overall misaligned behavior. TechCrunch also reported that the card shows improvement over Mythos 5 and Sonnet 5. Fable can help discover software flaws, but Anthropic does not mean it to develop exploits. Mythos access rules and the planned enterprise privacy system still need outside testing.
What to watch
Compare actual bills, latency, task completion, and false positive rates on customer workloads. Watch enrollment rules and audit records for Mythos access. Enterprise customers should verify where monitoring runs, who controls the logs, and whether the fall rollout keeps the promised privacy without weakening misuse detection.
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