appendSystemPrompt
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.
Forked background sessions are told to stay in their own worktree and never touch the original session's branch.
Not Anthropic's. This is the line from the earliest changelog entry here that named it, v2.1.221.
In the changelogs
12Releases whose published page names appendSystemPrompt.
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v2.1.269
Session/tool-use context object grows a large set of new accessors
The internal per-session context object gained many new fields covering effort, hooks, tools, and skills
found in this entry's text
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v2.1.260
get_context_usage no longer factors in appendSubagentSystemPrompt
Context-usage estimates for embedding hosts no longer count the subagent system-prompt append.
found in this entry's text
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v2.1.257
systemPromptSnapshot option for records the system prompt once per conversation
A systemPromptSnapshot option freezes the system prompt for a conversation, so mid-session changes wait for compaction.
found in this entry's text, named in this entry
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v2.1.257
New system prompt snapshot plumbed into MCP/tool context
The tool and agent context now exposes a snapshot of the system prompt in effect alongside the appended one.
found in this entry's text
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v2.1.252
New appendSubagentSystemPrompt option threaded through session/agent config
A new appendSubagentSystemPrompt option lets a subagent's system-prompt append differ from the main session's.
found in this entry's text
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v2.1.252
appendSubagentSystemPrompt threaded into more system-prompt construction call sites
Internal plumbing now threads a subagent-specific system prompt option through more call sites.
found in this entry's text
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v2.1.242
Command-line system prompts kept separate from resolved ones
Your typed --system-prompt values are kept apart from the resolved ones for cloud and remote setup.
found in this entry's text
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v2.1.225
SDK query context construction was consolidated
The non-interactive query path builds its context in one shared place, meant to behave identically.
found in this entry's text
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v2.1.221
Forked background sessions get clearer worktree guidance
Forked background sessions are told to stay in their own worktree and never touch the original session's branch.
named in this entry, found in this entry's text
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v2.1.136
Enterprise Managed Settings Helper
found in this entry's text
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v2.0.71
Improved Token Counting for Custom System Prompts
found in this entry's text
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v2.0.56
SDK Init Parameters for System Prompts and Agents
found in this entry's text
First cited
4The earliest release whose published evidence quoted appendSystemPrompt was v2.0.71, 16 Dec 2025. 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.
Presence across releases
0The 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.