Claude Opus 5 nails 20×20-digit multiplication with 1200/1200 accuracy at max reasoning
xeophon · x · 2026-09-17
In a simple eval shared by maksymandr and amplified by xeophon, Claude Opus 5 multiplied numbers up to 20×20 digits without any external tools, scoring a perfect 1200/1200 — but only with maximum reasoning enabled.
While the eval itself is trivial, the author argues it's newly relevant for measuring no-CoT (internal computation) capabilities, especially for recurrent-depth architectures, name-dropping GPT-6-Astra as an example. The community reaction was one of surprise.
Related event: Frontier LLMs Nail 20-Digit Multiplication Without Tools(9 posts)→
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