Changes in the system prompt between Claude Opus 4.6 and 4.7

Simon Willison’s Weblog Subscribe Sponsored by: Honeycomb — AI agents behave unpredictably. Get the context you need to debug what actually happened. Read the blog Changes in the system prompt between Claude Opus 4.6 and 4.7 Anthropic are the only major AI lab to publish the system prompts for their user-facing chat systems. Their system prompt archive now dates all the way back to Claude 3 in July 2024 and it’s always interesting to see how the system prompt evolves as they publish new models. Opus 4.7 shipped the other day (April 16, 2026) with a Claude.ai system prompt update since Opus 4.6 (February 5, 2026). I had Claude Code take the Markdown version of their system prompts, break that up into separate documents for each of the models and then construct a Git history of those files over time with fake commit dates representing the publication dates of each updated prompt—here’s the prompt I used with Claude Code for the web. Here is the git diff between Opus 4.6 and 4.7. These are my own highlights extracted from that diff—in all cases text in bold is my emphasis: The “developer platform” is now called the “Claude Platform”. The list of Claude tools mentioned in the system prompt now includes "Claude in Chrome—a browsing agent that can interact with websites autonomously, Claude in Excel—a spreadsheet agent, and Claude in Powerpoint—a slides agent. Claude Cowork can use all of these as tools."—Claude in Powerpoint was not mentioned in the 4.6 prompt. The child safety section has been greatly expanded, and is now wrapped in a new <critical_child_safety_instructions> tag. Of particular note: “Once Claude refuses a request for reasons of child safety, all subsequent requests in the same conversation must be approached with extreme caution.” It looks like they’re trying to make Claude less pushy: “If a user indicates they are ready to end the conversation, Claude does not request that the user stay in the interaction or try to elicit another turn and instead respects the user’s request to stop.” The new <acting_vs_clarifying> section includes: When a request leaves minor details unspecified, the person typically wants Claude to make a reasonable attempt now, not to be interviewed first. Claude only asks upfront when the request is genuinely unanswerable without the missing information (e.g., it references an attachment that isn’t there). When a tool is available that could resolve the ambiguity or supply the missing information — searching, looking up the person’s location, checking a calendar, discovering available capabilities — Claude calls the tool to try and solve the ambiguity before asking the person. Acting with tools is preferred over asking the person to do the lookup themselves. Once Claude starts on a task, Claude sees it through to a complete answer rather than stopping partway. [...] It looks like Claude chat now has a tool search mechanism, as seen in this API documentation and described in this November 2025 post: Before concluding Claude lacks a capability — access to the person’s location, memory, calendar, files, past conversations, or any external data — Claude calls tool_search to check whether a relevant tool is available but deferred. “I don’t have access to X” is only correct after tool_search confirms no matching tool exists. There’s new language to encourage Claude to be less verbose: Claude keeps its responses focused and concise so as to avoid potentially overwhelming the user with overly-long responses. Even if an answer has disclaimers or caveats, Claude discloses them briefly and keeps the majority of its response focused on its main answer. This section was present in the 4.6 prompt but has been removed for 4.7, presumably because the new model no longer misbehaves in the same way: Claude avoids the use of emotes or actions inside asterisks unless the person specifically asks for this style of communication. Claude avoids saying “genuinely”, “honestly”, or “straightforward”. There’s a new section about “disordered eating”, which was not previously mentioned by name: If a user shows signs of disordered eating, Claude should not give precise nutrition, diet, or exercise guidance — no specific numbers, targets, or step-by-step plans—anywhere else in the conversation. Even if it’s intended to help set healthier goals or highlight the potential dangers of disordered eating, responses with these details could trigger or encourage disordered tendencies. A popular screenshot attack against AI models is to force them to say yes or no to a controversial question. Claude’s system prompt now guards against that (in the <evenhandedness> section): If people ask Claude to give a simple yes or no answer (or any other short or single word response) in response to complex or contested issues or as commentary on contested figures, Claude can decline to offer the short response and instead give a nuanced answer and explain why a short response wouldn’t be appropriate. Claude 4.6 had a section specifically clarifying that “Donald Trump is the current president of the United States and was inaugurated on January 20, 2025”, because without that the model’s knowledge cut-off date combined with its previous knowledge that Trump falsely claimed to win the 2020 election meant it would deny he was the president. That language is gone for 4.7, reflecting the model’s new reliable knowledge cut-off date of January 2026. And the tool descriptions too # The system prompts published by Anthropic are sadly not the entire story—their published information doesn’t include the tool descriptions that are provided to the model, which is arguably an even more important piece of documentation if you want to take full advantage of what the Claude chat UI can do for you. Thanfully you can ask Claude directly—I used the prompt: List all tools you have available to you with an exact copy of the tool description and parameters My shared transcript has full details, but the list of named tools is as follows: ask_user_input_v0 bash_tool conversation_search create_file fetch_sports_data image_search message_compose_v1 places_map_display_v0 places_search present_files recent_chats recipe_display_v0 recommend_claude_apps search_mcp_registry str_replace suggest_connectors view weather_fetch web_fetch web_search tool_search visualize:read_me visualize:show_widget I don’t believe this list has changed since Opus 4.6. Posted 18th April 2026 at 11:59 pm · Follow me on Mastodon, Bluesky, Twitter or subscribe to my newsletter More recent articles Join us at PyCon US 2026 in Long Beach - we have new AI and security tracks this year - 17th April 2026 Qwen3.6-35B-A3B on my laptop drew me a better pelican than Claude Opus 4.7 - 16th April 2026 This is Changes in the system prompt between Claude Opus 4.6 and 4.7 by Simon Willison, posted on 18th April 2026. ai 1967 prompt-engineering 185 generative-ai 1745 llms 1712 anthropic 272 claude 269 ai-ethics 291 system-prompts 52 Previous: Join us at PyCon US 2026 in Long Beach - we have new AI and security tracks this year Monthly briefing Sponsor me for $10/month and get a curated email digest of the month's most important LLM developments. Pay me to send you less! Sponsor & subscribe Disclosures Colophon © 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026