Claude Fable 5.1
Released on September 1, 2026
Changes from previous version
Successor to Claude Fable 5 with stronger agentic coding, scientific research, computer use, and business workflows. Low and Medium effort already match or beat Fable 5 full-effort results at lower cost. Cache reads fall from $1/M to $0.25/M. Cyber safeguards flag about 60% fewer false positives, and Fable 5.1 can now be used to find software vulnerabilities (not to write exploits). Eligible customers can use zero data retention until Enterprise Frontier Safeguards roll out this fall.
Release Summary
Anthropic's most advanced generally available model for coding, knowledge work, and long-running problem-solving. Same underlying weights as Claude Mythos 5.1, with production safeguards. More than doubles Claude Fable 5 on Terminal-Bench-Science 0.1 (52.6% vs 24.7%) and AutomationBench (31.4% vs 17.1%), and leads Claude Opus 5 and GPT Sol 5.6 on the published agentic coding and knowledge-work suite. List API pricing stays $10/M input and $50/M output; cache reads drop 75% to $0.25/M, cutting typical token-billed workloads by about 25% and highly agentic ones by up to about 45%. Available as claude-fable-5-1 on the Claude API, Claude apps, Amazon Bedrock, Google Cloud, and Microsoft Azure. 1M-token context, 128k max output, knowledge cutoff June 2026.
Timeline
Claude Fable 5.1 released
Anthropic launches Fable 5.1 for general availability as claude-fable-5-1, with the same $10/$50 list rates as Fable 5 and cache reads cut to $0.25 per million tokens.