Opus 4.6 to 4.7 Prompt Changes
Simon Willison’s post treats system prompt diffing as a way to understand how Claude chat behavior changes between releases. The most consequential additions in Opus 4.7 center on acting vs clarifying, the new tool_search rule, stronger concision guidance, and expanded safety instructions.
How The Analysis Works
The post turns published prompt history into a diffable artifact, then extracts the changes most likely to affect real product behavior.
Reconstruct prompt history
Claude Code is used to create dated files and a git history from Anthropic’s published prompt archive.
Extract notable behavioral changes
The article highlights safety, verbosity, clarification, and tool-use changes rather than trying to summarize every diff line.
Interpret the product implications
Willison infers likely UI and interaction changes, including less pushiness and more willingness to act with tools before asking the user.
Supplement with tool inventory evidence
He then asks Claude directly for its tools and descriptions to expose capabilities missing from the published prompt archive.
The Biggest Prompt Changes
The post emphasizes changes that alter how the product handles ambiguity, refusal, verbosity, and controversial or safety-sensitive requests.
Acting vs clarifying
Opus 4.7 is instructed to make a reasonable attempt with tools when details are minor rather than interrogating the user first.
tool_search rule
The model should now verify tool availability before saying it lacks access to information or capabilities.
Verbosity guidance
The prompt now explicitly encourages concise answers to avoid overwhelming users with unnecessary length.
Safety And Moderation Changes
The newer prompt expands its safety posture and adds more explicit rules for repeated refusals and nuanced handling of sensitive topics.
Child safety expansion
The child-safety section is expanded and tagged more formally, with stronger follow-on caution after child-safety refusals.
Disordered eating guidance
A new section explicitly prohibits precise nutrition, diet, or exercise targets in conversations that show signs of disordered eating.
Evenhandedness short-answer guardrail
The system prompt now pushes back on simplistic yes-or-no responses to complex or contested issues.
Developer platform renaming
Even terminology changes are tracked because they hint at product and branding shifts inside Anthropic’s system instructions.
The Missing Layer: Tool Descriptions
Willison’s main meta-point is that published system prompts are only part of the story. The model’s tool layer may shape real behavior even more.
Tool descriptions gap
The public prompt archive omits tool descriptions, leaving an incomplete picture of how Claude chat actually behaves.
Claude tool inventory
The shared transcript reveals named tools including tool_search, web_search, web_fetch, bash_tool, image_search, and several UI or connector surfaces.
Claude Code
Claude Code is not just mentioned as a product, but used as the actual analysis instrument for reconstructing the prompt archive and diffs.
FAQ From The Knowledge Graph
The generated graph includes linked Question and Answer nodes for the article’s main interpretive points.
What new tool-related instruction does the article highlight?
Claude should call tool_search before claiming it lacks access to information or capabilities.
How does the article say Claude is being nudged on verbosity?
The prompt now explicitly pushes for focused, concise answers.