Anthropic has made an unexpected but logical move by releasing Claude Fable 5.1. This is not just an iterative update to the flagship model, but a strategic response to one of the industry's most pressing problems—intellectual property theft through distillation. Alongside the new version, the company has introduced unprecedented protection that blocks the ability to "rewrite the history" of conversations for new developer accounts, while preserving the model's original reasoning logic.
The release took place on Tuesday, and alongside the full version of Fable 5.1, its lightweight modification—Mythos 5.1—was also introduced. Both models are already available on all key cloud platforms, including Amazon Bedrock, Google Cloud, and Microsoft Foundry, signaling Anthropic's readiness for large-scale industrial deployment.
Price Unchanged, but Savings Are Obvious
Base rates remain the same: $10 per million input tokens and $50 per million output tokens. However, the real savings for developers lie in the details. The cost of cache reads has been radically reduced by 75%—down to $0.25 per million operations. In my estimation, this makes the model significantly more attractive for tasks with a high degree of query repetition.
Anthropic emphasizes that typical scenarios now cost 25% less, while complex agentic tasks requiring deep planning offer up to 45% savings. This is a serious bid for leadership in the price war for enterprise clients.
Breakthrough Benchmark Results
Particular attention deserves the progress in scientific and engineering disciplines. In the Terminal-Bench-Science 0.1 test, the model achieved a staggering 52.6%, whereas the previous version, Fable 5, barely reached 24.7%. More than a twofold increase—this is not evolution but a true leap.
In general programming, the results are also impressive: 55.8% in Terminal-Bench 4.0 versus 52.3% for Opus 5 and 37.3% for GPT-5.6 Sol from OpenAI. Especially telling is the twofold growth in AutomationBench (up to 31.4%), indicating a significant improvement in the model's ability to autonomously execute business processes. The model's knowledge base now covers data up to June 2026.
The War on Distillation: A New Reality
The key innovation is copy protection, which is directly linked to Anthropic's investigation. The company identified over 16 million conversations related to distillation through approximately 24,000 fake accounts. Three Chinese labs were named outright: DeepSeek, Moonshot AI, and MiniMax. Moonshot accounted for 3.4 million requests.
The restriction applies only to accounts created after August 31. Existing users of Claude Code, Cowork, and Claude.ai will not notice any changes. This is a smart phased approach that does not break current workflows but creates a barrier for future copying attempts.
My analysis: this step is just the beginning. I am confident that in future versions, Anthropic will tighten checks for all accounts. The company clearly intends to protect its competitive advantages, and the market should be prepared for such measures to become an industry standard. While Fable 5 will remain available until June 2027, support for Fable 5.1 is guaranteed at least until September 2027. This gives developers ample time to migrate without haste.