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Archived response·drift

Claude Opus 5 on D1, 2026-09-11

Scored answered · correct · format ok — correct if the response answers [No] (91 = 7 × 13).

Model: anthropic/claude-opus-5
pinned anthropic/claude-opus-5-20260723; alias resolved to anthropic/claude-opus-5-20260723 at 2026-09-11 09:00:01 UTC (matches the pin)
Prompt: D1 (drift)
Date: 2026-09-11 · run 20260911T090002Z-da0dd3 · scorer v1
Permalink: https://modeldrift.watch/r/2026-09-11/D1/anthropic/claude-opus-5/

Prompt D1sent verbatim

Is 91 a prime number? Think step by step and then answer "[Yes]" or "[No]".

Why this prompt Composite that looks prime (7x13). Scores correctness, CoT presence, bracket format.

Scored: answered · correct · format ok
Received: 2026-09-11 09:00:11 UTC
Run: 20260911T090002Z-da0dd3
Served by: Claude Platform on AWS · HTTP 200 · finish stop
Size: 380 characters · 214 tokens out incl. hidden reasoning · 6.1 s

Highlighted: the last [Yes]/[No] bracket, which is the scored answer (No).

**Step 1: Check what 91 is divisible by.**
- Is it even? No, 91 is odd, so 2 doesn't divide it.
- Digit sum: 9 + 1 = 10, not divisible by 3, so 3 doesn't divide it.
- Does it end in 0 or 5? No, so 5 doesn't divide it.
- Divide by 7: 7 × 13 = 91. ✓
**Step 2: Conclusion.**
Since 91 = 7 × 13, it has divisors other than 1 and itself, so it is a composite number, not prime.
[No]

End of response · 12 lines · 380 characters · sha256 ce516624f096f3c6f12af5b04bbe817b62049fa564e696daa84980160ecc292d

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