Anthropic lifts the veil on the latest features for Fable 5.2 & Mythos 5.2

• Anthropic releases Fable 5.2 and Mythos 5.2 designed to help solve complex problems and ambitious projects
• Both offer a 20% cheaper token cost than previous versions
• The models are highly capable across coding, biology scientific and mathematics research

Anthropic’s latest Fable and Mythos releases have been unveiled, offering users superior outputs that are more accurate at a cheaper token cost than previous versions.

Fable 5.2 is available for all users and couples its improved inference with an improved set of cybersecurity and biology safeguards. But to get your hands on the expanded capabilities of Mythos 5.2, you’ll have to apply through Anthropic’s Life Sciences and Cyber Verification Programs.

Anthropic totes the new Fable and Mythos versions as being perfect for “ambitious, open-ended technical work” rather than as a “daily driver” — for which Anthropic recommends sticking to Opus 5.5.

Cheaper, quicker, and more accurate

The latest Fable release promises more bang for your buck over the 5.1 release. Anthropic says that 5.2 usage will sit at $8 per million input tokens and $40 per million output tokens — around 20% cheaper than the previous version.

But if you’re on a deadline or just want something done quickly, Anthropic is introducing an optional “fast mode” that increases token generation speed by up to 2.5 times at an increased cost of $16 (input) and $80 (output) per million tokens.

Across almost every benchmark task, Anthropic says Fable 5.2 is more accurate than Opus 5.5, delivering results faster and more accurately with a significantly reduced token cost per task.

But Anthropic says users will be best served by taking a balanced approach to model use, using Opus 5.5 to get tasks started with Fable 5.2 coming on board as an “advisor” for more difficult tasks.

To demonstrate its capabilities, one of Anthropic’s engineers gave Fable 5.2 the task of designing a prototype operating system. Over the course of eight days over 1,000 agents were writing, testing, and reviewing code, from which the model produced a working operating system that boots and contains all the necessary bells and whistles including built-in Claude functionality.

“Claude Fable 5.2 is great for taking a loose idea and refining it. Its answers are really well considered, and within a few turns I can almost always say “ok, go do that,” and trust that it’ll complete it with little intervention,” said Tom Pritchard, Staff Engineer, Shopify. “It feels like working with another staff-level engineer.”

Anthropic’s engineers demonstrated Fable’s capabilities across science and mathematics using a range of tasks. According to Anthropic, Fable 5.2 was able to formalize the proof of Fermat’s Last Theorem in 30 hours, designed a home voice-assistant hub, a USB speakerphone, and a handheld virtual pet from scratch, and solved two open problems in black hole physics.