Anthropic has officially launched its fifth-generation flagship model, Claude Fable 5, now fully available on platforms like Claude API, AWS Amazon Bedrock, and Google Cloud. As the public, compliance-friendly version of the previously restricted Mythos model (due to cybersecurity risks), the release of Fable 5 directly challenges OpenAI GPT-5.5's dominance in long-cycle agentic tasks. The model comes with a default 1M context input window and supports up to 128k tokens in a single output, marking a new technological era for large-model long-range reasoning and asynchronous automated workflows. When it comes to engineering details and pricing, Anthropic has adopted an aggressive market strategy. The API pricing for Fable 5 is set at $10 per million input tokens and $50 per million output tokens. This pricing shatters previous rumors that "Mythos-level models must cost over $100," with usage costs coming in at less than half of competitor OpenAI GPT-5.5 Pro (which charges $60 for large input volumes and $270 for output). Additionally, Anthropic announced that until June 22, existing Pro, Max, and Team subscription users can try Fable 5 at no extra cost. However, starting June 23, the model will be removed from subscription bundles and will transition to a fully usage-based point system for billing. That said, the high cost-effectiveness comes with complex engineering trade-offs and anti-abuse measures. To mitigate potential weaponization risks of Mythos-level models in fields like biology, chemistry, and cybersecurity, Anthropic has implemented a new real-time streaming safety classifier in Fable 5. If the system detects that a user’s input request triggers a compliance red flag, Fable 5 will seamlessly redirect the conversation on the front end, automatically downgrading the response to the next-strongest model, Claude Opus 4.8. This "strong model detection, fallback to next-strongest model" mechanism ensures large-scale commercial accessibility by sacrificing extreme edge use cases. However, it also introduces new technical challenges for developers seeking consistent performance in specific vertical domains.