Anthropic released Claude Fable 5, its first widely available Mythos-level AI model, on June 9, 2026. The model is designed to handle complex, long-duration tasks including software development, scientific research, data analysis, and visual understanding [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11].
Claude Fable 5 incorporates strict security measures to prevent misuse in cyberattacks against critical infrastructure such as banks and power grids. About 5% of queries involving cybersecurity, biotechnology, or AI model distillation are automatically redirected to the lower-capability Claude Opus 4.8 model to reduce abuse risk. Anthropic said this safeguard maintains broad general use while limiting potential harm [1, 3, 4, 5, 7, 8, 9, 11].
The Fable 5 model costs $10 per million input tokens and $50 per million output tokens, roughly twice the price of Opus 4.8. Despite the pricing, it outperforms major competitors in software engineering benchmarks, including Hex and SWE-Bench-Pro tests, scoring higher than OpenAI’s GPT-5.5 and Google’s Gemini 3.1 Pro [3, 6, 7, 8].
Some critics allege Anthropic secretly restricts developer and advanced AI research functionalities in Fable 5, without clear notification. Open researcher Nathan Lambert called this a "horrifying" limitation harming progress and safety. However, Anthropic and other sources note that only about 5% of sensitive queries are redirected and the majority of users experience full model capabilities [7, 8, 9, 11].
Anthropic also offers Claude Mythos 5, a professional AI variant with fewer restrictions intended for government, defense, and specialized research groups. Access to Mythos models is regulated through partnerships with U.S. government agencies amid ongoing legal disputes with the Trump administration [3, 6, 7, 8, 9].
The company pays $1.25 billion monthly to lease data center capacity from Elon Musk’s xAI/SpaceX to meet the compute demands of its large models. Competition in the AI market is intensifying with Anthropic accelerating enterprise deployments and preparing for an IPO alongside rivals like OpenAI [3, 7].
Anthropic plans to gradually restore Fable 5 access to subscription tiers as compute capacity improves and expand Mythos model availability to more organizations under a "trust access" framework in the future [7, 8, 9, 11]. The rollout of these new access models is expected in the coming months.
