Anthropic has released Claude Fable 5.2 and Claude Mythos 5.2. Both products use the same underlying model designed for complex work in software engineering, mathematics, and physical sciences. Fable 5.2 includes built in safety measures for public access, while Mythos 5.2 is limited to approved research partners working in cybersecurity and life sciences.

The 5.2 update generates text up to 30 percent faster than version 5.1. Standard pricing is set at 8 dollars per million input tokens and 40 dollars per million output tokens. Users can also select an optional fast mode that boosts speed up to 2.5 times for 16 dollars per million input tokens and 80 dollars per million output tokens. Benchmark evaluations by Artificial Analysis scored Fable 5.2 at 65 on its Intelligence Index across tasks using its 1M token context window.

Anthropic reported using Fable 5.2 internally to rewrite core production services from Python to Rust, producing software that starts about 26 times faster. In another experiment, an engineer tasked the model with building a working operating system from an empty folder, which Fable 5.2 completed in eight days using over 1,000 subagents.

Why it matters

For developers and creators, Fable 5.2 serves as a high level technical coordinator that can manage large projects or advise smaller models like Sonnet and Haiku. Although independent tests show it runs slower per task and uses more tokens than average daily models, its deep problem solving helps automate complex migrations and system design.

Try it yourself

Use this prompt to outline a complex technical project before building it with AI.

Act as a senior system architect. Review this project goal: [insert project description]. Break the work into logical phases, outline key hardware or software dependencies, identify major technical risks, and write clear prompts for a coding assistant to build each phase step by step.