While Fable 5 excels in long-term tasks, its complex processes can lead to slower performance. The AI market’s increased focus on reasoning is driving up the cost of these models.
June 9, 2026
As it continues to target cybersecurity, AI lab Anthropic on Tuesday introduced two new models, demonstrating how it is improving capabilities such as reasoning and providing tools to help cyber defenders.
Claude Fable 5 is a Mythos-class model, according to Anthropic -- a reference to the original Mythos, which is still in restricted release due to its reputed ability to easily find and exploit security holes in software. While the model is adept at cybersecurity tasks, Anthropic has restricted its use due to the risk of misuse as a cyber threat.
As a general-use model, Fable 5 shows impressive performance in areas such as software engineering, knowledge work, vision and scientific research. The AI lab also introduced Claude Mythos 5, which will be deployed through Project Glasswing, a vendor-led security initiative in collaboration with select companies and the U.S. government.
