Changes in the system prompt between Claude Opus 4.6 and 4.7
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| Source: HN | Original article
Anthropic rolled out Claude Opus 4.7 on April 16, 2026, and with it a revised system prompt that diverges noticeably from the February 5 release of Opus 4.6. The company’s newly opened prompt archive now logs every system prompt back to Claude 3 in July 2024, letting observers trace how the hidden instruction set has been tweaked across model generations.
The updated prompt shifts the model’s internal “thinking” policy. Where Opus 4.6 always emitted a fixed‑verbosity response and populated the “thinking” field with a full chain‑of‑thought, Opus 4.7 calibrates response length to task complexity and leaves the thinking field empty unless the user explicitly opts in. The change is documented in the latest Claude API migration guide and reflected in the “Prompting best practices” page, which now advises developers to request more or less deliberation with explicit cues such as “Think carefully and step‑by‑step before responding.”
Why it matters is twofold. First, prompt engineers who have hard‑coded cues for Opus 4.6 will see altered behavior on 4.7, potentially breaking production pipelines that rely on predictable verbosity or automatic chain‑of‑thought output. Second, the tighter coupling between system prompt and model output raises the stakes for security‑sensitive applications; the omission of default thinking blocks could hide internal reasoning that some compliance frameworks previously audited.
What to watch next are the rollout of Anthropic’s migration checklist and the impact on Claude Code, which we evaluated in our April 19 piece “Is Claude Opus 4.7 the Best AI Coding Model Right Now?”. Early adopters should run the checklist, test prompt rewrites, and monitor Anthropic’s forthcoming updates to the prompt archive, which may signal further shifts in model alignment or new developer‑facing controls.
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