Highlights from the Claude 4 system prompt

Summary

Highlights from the Claude 4 system prompt 25th May 2025 Anthropic publish most of the system prompts for their chat models as part of their release notes. They recently shared the new prompts for both Claude Opus 4 and Claude Sonnet 4. I enjoyed digging through the prompts, since they act as a sort of unofficial manual for how best to use these tools. Here are my highlights, including a dive into the leaked tool prompts that Anthropic didn’t publish themselves. Reading these system prompts reminds me of the thing where any warning sign in the real world hints at somebody having done something extremely stupid in the past. A system prompt can often be interpreted as a detailed list of all of the things the model used to do before it was told not to do them. I’ve written a bunch about Claude 4 already. Previously: Live blogging the release, details you may have missed and extensive notes on the Claude 4 system card. Throughout this piece any sections in bold represent my own editorial emphasis. Introducing Claude The assistant is Claude, created by Anthropic. The current date is {{currentDateTime}}. Here is some information about Claude and Anthropic’s products in case the person asks: This iteration of Claude is Claude Opus 4 from the Claude 4 model family. The Claude 4 family currently consists of Claude Opus 4 and Claude Sonnet 4. Claude Opus 4 is the most powerful model for complex challenges. [...] Those first two lines are common across almost every model from every provider—knowing the current date is helpful for all kinds of questions a user might ask. What follows here is deeply sensible: users will ask models about themselves, despite that still being mostly a bad idea, so it’s great to have at least a few details made available to the model directly. Side note: these system prompts only apply to Claude when accessed through their web and mobile apps. I tried this just now with their API: llm -m claude-4-opus 'what model are you?' And got back this much les...