Anthropic launches Claude Fable 5.1

Fable 5.1 is less a benchmark flex than a bet that useful AI agents must work for hours without bankrupting their operators.

• –The 1M-token context and 128K output ceiling suit repository-scale coding, multistep research, and large document workflows.
• –Cache reads fall from $1 to $0.25 per million tokens, improving persistent-agent economics, though uncached usage remains premium-priced at $10 input and $50 output per million tokens.
• –Anthropic says typical workloads may cost about 25% less and highly agentic workloads up to 45% less, making task-completion cost more important than headline token pricing.
• –Developers migrating from Fable 5 must account for breaking changes involving forced tool use, thinking blocks, and edited conversation history.