Anthropic doubles a science benchmark score with Fable 5.1 while OpenAI says its Astra model crosses critical cyber threshold

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Anthropic released Claude Fable 5.1 and Claude Mythos 5.1 on September 1, the latest interaction of the model series that is among the most influential, and expensive, model launches in recent memory.

Now, with the launch of the two new models, Anthropic is claiming significant jumps in performance on scientific benchmarks. On Terminal-Bench-Science 0.1, an agentic scientific research benchmark, the company reports Fable 5.1 at 52.6% against 24.7% for Fable 5, 29.0% for Claude Opus 5 and 22.4% for GPT-5.6 Sol. Anthropic puts the standard error at 3.5 to 4.5 points per model.

The Terminal-Bench-Science 0.1 benchmark covers 70 scientist-contributed workflows across the life, physical, Earth, mathematical and engineering sciences. Agents work in self-contained terminal environments and submit artifacts graded against hidden tests.

On the same day, OpenAI reported that one configuration of its forthcoming Astra model scored 100% on the public ExploitBench benchmark, which tests whether models can develop exploits for known vulnerabilities. To address possible benchmark contamination, the company created an internal version containing 20 high-severity V8 vulnerabilities disclosed between June and August 2026. The company still plans on releasing a form of the model publicly with enhanced safeguards, noting: “We plan to make Astra available soon, but access to its most advanced cybersecurity capabilities will be more limited.”