Anthropic upgrades Claude Fable and Mythos as it prepares an IPO

Anthropic says it upgraded Claude Fable and Claude Mythos, models designed for daunting technical challenges, and that the new versions improve coding, reasoning and vision.[1] During prerelease testing, the company says engineers used them to complete software migrations they considered otherwise infeasible, design three working electronic devices and solve two open physics problems about black holes.[1] Anthropic also says a model coordinated more than 1,000 subagents around the clock for eight days.[1] It reports that more than 90% of changes merged into its core codebase are now written by Claude with human guidance.[1]

Anthropic says Fable and Mythos share the same underlying model, but Fable has stronger cybersecurity and biology safeguards so it can be broadly available.[1] The company says those safeguards are as robust as Fable 5.1’s while producing fewer unnecessary blocks.[1] CNBC reports that Fable 5.2 is generally available and Mythos 5.2 requires verification.[2] Organizations pursuing beneficial cybersecurity or biomedical research can apply for Mythos through Anthropic’s verification programs.[1] Anthropic recommends Claude Opus 5.5 for most coding and knowledge tasks.[1] It lists prices of $8 per million input tokens and $40 per million output tokens, and says outputs are up to 30% faster than the prior versions.[1]

Anthropic says Fable 5.2 scored 49.1% at Xhigh effort, the highest score among released models it had tested.[1] At High effort, the company says Fable 5.2 scored about as well as Opus 5.5 at its best score for roughly half the per-task cost.[1] At Max effort, it reports a score of 83.5, ahead of Opus 5.5 and Fable 5.1.[1] Anthropic says it developed new evaluations to examine concerning behaviors such as sandbox escapes.[1] It believes high-stakes misalignment risks remain low and says the model performed as well as or better than recent models on most alignment measures.[1] These are company-reported evaluations and judgments.

Anthropic’s proposed IPO consists of 825 million Class A shares: 801,351,354 sold by the company and 23,648,646 by existing stockholders.[3] The company expects to give underwriters a 30-day option to buy up to an additional 123.75 million shares.[3] Anthropic expects a price range of $70 to $78 per share and has applied to list on Nasdaq under the symbol ANT.[3] CNBC reported that Anthropic was aiming for an IPO valuation of $1 trillion to $1.5 trillion, below a previously floated $2 trillion target.[2] Anthropic said it generated $33.24 billion in revenue in the nine months through September 30, roughly 1,200% more than in the same period a year earlier.[2]