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FrontierThe story, in brief

Changes in the system prompt between Claude Opus 4.6 and 4.7

Claude 4.7's system prompt just changed. Here's what Anthropic is optimizing for.

Reporting by Simon Willison 1 min brief
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The KeyNews take

Why it matters

System prompt modifications between model versions reveal shifting priorities in model behavior, safety guardrails, and instruction-following — a leading indicator of capability direction and alignment strategy.

The key facts

9 to know

  1. Claude Opus 4.6 to 4.7 system prompt differences documented

  2. Published Apr 18, 2026 on simonwillison.net (reputable AI researcher)

  3. System prompt analysis as proxy for model alignment and behavior tuning

  4. Anthropic's evolving approach to instruction handling between versions

  5. Claude Opus 4.6 → 4.7 system prompt divergence detected

  6. Changes documented by independent researcher (Simon Willison)

  7. Anthropic has not publicly announced system prompt modifications

  8. Implies undocumented behavioral shifts between minor versions

  9. UNVERIFIED - no official Anthropic statement provided

Go to the source

Simon Willisonsimonwillison.net

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