Anthropic releases Claude Fable 5.1 and Claude Mythos 5.1

Anthropic

Models / LLM official 1 src. ~1 min

On September 1 Anthropic released Claude Fable 5.1 (claude-fable-5-1 on API, AWS, Google Cloud, Azure) and its reduced-safeguards twin Mythos 5.1, limited to vetted US cyberdefenders and life-sciences programs. Benchmarks include 55.8% Terminal-Bench 4.0 (60.9% for Mythos) and 73.4% CursorBench 3.2.0; pricing stays $10/$50 per M tokens with cache reads cut 75% to $0.25/M, making typical workloads ~25% cheaper than Fable 5.

Why it matters

Frontier coding model drop with a two-tier safeguards split

Importance: 4/5

Anthropic frontier release; new default coding model with a safeguards split

anthropic claude claude-fable-5-1 claude-mythos frontier-model release pricing 1m-context

Sources

official Introducing Claude Fable 5.1 and Claude Mythos 5.1