Anthropic Launches Claude Fable 5.1: Can It Stop AI Copycats?

Anthropic released Claude Fable 5.1 on Tuesday, and the model ships with a lock on its own reasoning. New developer accounts can no longer rewrite a conversation's history while keeping Claude's stored thinking in place.

The company calls Fable 5.1 and its restricted sibling Mythos 5.1 the world's most advanced models for coding and knowledge work. Both went live across Anthropic's platform, Amazon Bedrock, Google Cloud and Microsoft Foundry.

What Claude Fable 5.1 costs and scores

Headline pricing has not moved. Fable 5.1 still costs $10 per million input tokens and $50 per million output.

The savings sit elsewhere. Cache reads fall 75% to $0.25 per million. Anthropic puts typical workloads 25% cheaper, and complex agent tasks up to 45% cheaper.

Anthropic's own scorecard shows the sharpest gain in agentic science work. Fable 5.1 hit 52.6% on Terminal-Bench-Science 0.1, more than double Fable 5's 24.7%.

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