systemPromptSnapshot

A Claude Code settings key, read out of the shipped bundle. It was in the build from v2.1.315 and was gone by v2.1.317.

Releases whose published page names systemPromptSnapshot.

1. v2.1.280 22 Sep 2026
   Custom system prompt updates now apply only after compaction (unless systemPromptSnapshot:false)

   SDK custom system prompt updates now apply after the next compaction, not the next turn

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

2. v2.1.274 16 Sep 2026
   System-prompt hot-swap now takes effect from the next turn, not at next compaction

   Swapping the system prompt mid-session now applies from the next turn instead of waiting for compaction

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

3. v2.1.274 16 Sep 2026
   Headless SDK sessions now detect and re-inject a changed system prompt mid-session

   Headless SDK sessions now detect a changed system prompt mid-session and re-inject it into the transcript

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

4. v2.1.260 3 Sep 2026
   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

5. v2.1.259 2 Sep 2026
   Background sessions get a narrower permission snapshot

   Background sessions run with session allow-rules cleared and a narrower set of working directories, and always snapshot the system prompt.

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

6. v2.1.257 1 Sep 2026
   New --system-prompt-snapshot CLI/agent option

   A new --system-prompt-snapshot option makes a session record its system prompt once and reuse it on resume.

   found in this entry's text

7. v2.1.257 1 Sep 2026
   New hideLoginNotice session option

   A new hideLoginNotice option lets a host session hide the login notice without hiding all welcome chrome.

   found in this entry's text

8. v2.1.257 1 Sep 2026
   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.

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

9. v2.1.257 1 Sep 2026
   get_context_usage command gains detail level and system-prompt snapshot input

   Context-usage requests can specify a detail level and pin the system prompt snapshot used for the calculation.

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

10. v2.1.257 1 Sep 2026
    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, named in this entry

The earliest release whose published evidence quoted systemPromptSnapshot was v2.1.257, 1 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.

One row per release since the first build this name was read out of. Absent means the build was read and the name was not in it, never mined means no bundle for that release was ever archived, and a declared type or a default is only ever what that release's own bundle stated.

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.