appendSystemPromptHead

A Claude Code settings key, read out of the shipped bundle. No mined inventory carries it: everything below comes from what this site has written about it.

Releases whose published page names appendSystemPromptHead.

1. v2.1.284 28 Sep 2026
   A new setting can carry text into the start of the system prompt

   Claude Code now passes a new value, appendSystemPromptHead, from startup into how it builds the system prompt, including in non-interactive runs

   named in this entry, found in this entry's text

2. v2.1.284 28 Sep 2026
   Part of an appended system prompt can now sit in the cached section

   A new appendSystemPromptHead option can move the start of an appended system prompt into the part of the prompt that is cached

   named in this entry, found in this entry's text

3. v2.1.284 28 Sep 2026
   SDK sessions pass along a new option for the start of the system prompt

   Non-interactive and SDK sessions now pass along an appendSystemPromptHead option, and the app connection gains a composer hook

   named in this entry, found in this entry's text

The earliest release whose published evidence quoted appendSystemPromptHead was v2.1.284, 28 Sep 2026. That is the oldest release this project wrote about it, so it is a floor on the name's age and not the release that introduced it. It is not a presence reading: which builds carried the name is the table below.

The miner has never read a build containing this name. It is here because a changelog entry of ours names it, which is evidence that it existed and not evidence of which releases carried it. The inventory starts at v2.1.138 and everything older than that was never mined.

Read out of the published npm bundle release by release, and out of Anthropic's own documentation as this site captured it. Nothing on this page is a description anybody here wrote about what the settings key does. All settings keys.