Unclear The condition that switches this step on and its visible effect are not known.
What
Before preparing the details of which tools are available, Claude Code now records how messages to the model should be formatted, including how tool changes are announced. In bare or CLAUDE_CODE_SIMPLE mode, the order of attachments (extra context added to a message) has also changed.
Why
This can change how notices about tool changes are sent to the model.
Names in the bundleCLAUDE_CODE_SIMPLE
The entry above is what we published on the day. These lines were added later, as Anthropic's own pages caught up, and they sit beside the original rather than replacing it.
Confirmed since
Anthropic's documentation has since written up CLAUDE_CODE_SIMPLE, on Output styles.
* On the full system prompt, custom output styles leave out Claude Code's section of built-in software engineering instructions, such as how to scope changes, write comments, and verify work, unless `keep-coding-instructions` is set to `tr…output-styles see the edit
Added since
A small documentation edit on Modifying system prompts touched a line naming CLAUDE_CODE_SIMPLE after this was published.
A custom output style leaves the `claude_code` preset's software engineering instructions out and uses your own. To keep them and layer your instructions on top, set `keep-coding-instructions: true` in the frontmatter. Those instructions a…agent-sdk/modifying-system-prompts see the edit
Something disagreesSomething we can check disagrees with this entry, or the writer said they could not settle it.
The writer flagged doubt
The condition that switches this step on and its visible effect are not known.
Anthropic's documentation agrees
A small documentation edit on Modifying system prompts touched a line naming CLAUDE_CODE_SIMPLE after this was published.