🚀 Anthropic has released Claude Fable 5 - the fifth generation of models designed for the longest and most complex tasks.
The main idea is a model that can handle tasks for days. In an agent harness like Claude Code, it plans work in stages, delegates subtasks to sub-agents, and checks the results itself: it writes tests for its code and uses vision to compare the output with the original design.
Fable 5 is at the Mythos level, the top of the line. The focus is on coding (large migrations, multi-day autonomous sessions) and enterprise tasks, where a large project can be handed over entirely and then the final result can be checked, rather than monitoring every step.
The main issue: from June 23, Fable 5 will not be available by subscription. Access is only consumption-based - you pay for tokens. The price is steep: $10 per million input tokens and $50 for output, with a 90% discount on prompt caching. Available through the Claude API (claude-fable-5), on a consumption-based Enterprise plan, as well as in AWS, Google Cloud, and Microsoft Foundry.
An interesting security detail: requests related to cybersecurity and biology are automatically redirected to Opus 4.8, and no Fable charge is applied for these switched requests.
