“Anthropic has launched Claude Fable 5.1 and Claude Mythos 5.1, its newest AI models aimed at coding, knowledge work, and scientific research." Plus the caption's supporting assertions: ~25% cheaper for typical workloads and up to 45% for highly agentic tasks, strong coding and research benchmarks, vulnerability identification, a…”

Anthropic's own announcement page confirms the release of Claude Fable 5.1 and Claude Mythos 5.1 and states that Fable 5.1 is generally available while Mythos 5.1 is available only through trusted access programs, with safeguards designed for cybersecurity and life sciences work. Anthropic describes Mythos 5.1 as "identical to Fable 5.1, but it offers more permissive safeguards for vetted individuals and organizations." The Amazon Bedrock model card for Mythos 5.1 records a model launch date of September 1, 2026, and AWS separately announced Fable 5.1 as generally available on Bedrock and Claude Platform on AWS. On pricing, Anthropic's Fable product page states that Fable 5.1 is priced at $10 per million input tokens and $50 per million output tokens, that cache reads now cost $0.25 per million tokens, 75% less than Fable 5, and that this "reduces the cost of typical workloads by an estimated 25% and highly agentic workloads by up to approximately 45%." Base input and output prices are unchanged from Fable 5. Anthropic's reported benchmark figures, from its own table: Terminal-Bench-Science 0.1 at 52.6% for Fable 5.1, versus 24.7% for Fable 5, 29.0% for Opus 5, and 22.4% for GPT-5.6 Sol, with a stated standard error of 3.5 to 4.5 points per model. Terminal-Bench 4.0: Fable 5.1 at 55.8%, Mythos 5.1 at 60.9%, Opus 5 at 52.3%, Fable 5 at 42.0%, GPT-5.6 Sol at 37.3%. CursorBench 3.2: 73.4% for Fable 5.1 versus 70.5% and 70.0%. Anthropic notes the model was evaluated with production safeguards active and that safeguard interventions were scored as zero, which it says likely understates raw capability. On science, Anthropic reports that Fable 5.1 trained a neural network producing a higher-resolution elevation map covering roughly one third of Venus from 30-year-old NASA Magellan radar data, sharpening detail from about 10 to 20 km to about 2 to 3 km, and that Mythos 5.1 designed experimentally validated protein binders with a hit rate near 50% across 12 targets, validated by two external organizations. On safeguards, Anthropic states that Fable 5.1 permits source-code vulnerability discovery but not exploit development, and reports roughly 60% fewer cyber safeguard interventions per session in Claude Code and 85% fewer biology false positives on benign requests. The one substantive independent counterweight: Artificial Analysis, which disclosed that it supported Anthropic with pre-release evaluation, measured Fable 5.1 at 66 on its Intelligence Index at max effort, the highest score it had measured, ahead of Opus 5 at 63, Fable 5 at 62, and GPT-5.6 Sol at 61. The same evaluation found Fable 5.1 at max effort costs $3.76 per Intelligence Index task versus $3.14 for Fable 5, about 20% more, because it uses roughly 1.7x the output tokens, so the cache read cut only partly offsets higher generation cost.