Anthropic releases updated Claude Fable and Mythos models

Anthropic says it upgraded Claude Fable and Claude Mythos for demanding technical challenges, with improvements in coding, reasoning and vision.[1] The company says the new models generate outputs up to 30% faster than Fable 5.1 and Mythos 5.1.[1] Anthropic lists prices of $8 per million input tokens and $40 per million output tokens.[1] An optional fast mode, which Anthropic says can speed token generation by up to 2.5 times, costs $16 per million input tokens and $80 per million output tokens.[1] CNBC reports the new models cost 20% less than the 5.1 generation.[2]

Anthropic says Fable has cybersecurity and biology safeguards that allow it to be available to all users.[1] The company says Fable 5.2’s safeguards are as robust as Fable 5.1’s while causing fewer unnecessary blocks.[1] Mythos has a narrower access path: Anthropic says organizations pursuing beneficial cybersecurity or biomedical research can apply through its verification programs, and says Mythos 5.2 is available only to organizations verified through those programs.[1][3]

Anthropic says the models helped its engineers complete software migrations it considered otherwise infeasible, designed three working electronic devices from scratch, and solved two open problems in black-hole physics.[1] It also says the models formalized a proof of Fermat’s Last Theorem in 30 hours.[1] In Anthropic’s FrontierCode 2.0 testing, Fable 5.2 scored 49.1% at Xhigh effort, the highest score among released models the company tested.[1] In early testing, Anthropic says Fable 5.2 at High effort scored about level with Opus 5.5 at Max effort for roughly half the cost per task.[1]

CNBC reported that Amodei called for slowing the pace of AI development in September, and that this release was Anthropic’s first frontier-model launch since then.[2] Anthropic responded, “We called for pacing, not pausing.”[2] CNBC also reported that Anthropic was preparing for a potentially historic IPO that could take place as soon as the following week, and was aiming for a $1 trillion to $1.5 trillion valuation.[2] Anthropic says it implemented its strongest-ever protections against distillation attacks.[1] The evidence does not establish that an IPO will occur or that the targeted valuation will be achieved.