CLAUDE_CODE_PLAIN_DELTA_FAST_PATH
A Claude Code environment variable, read out of the shipped bundle. It has been in the build since v2.1.311, including the newest one read.
Setting CLAUDE_CODE_PLAIN_DELTA_FAST_PATH turns on a quicker way of passing along plain streamed text when Claude Code runs without its interactive screen
Not Anthropic's. This is the line from the earliest changelog entry here that named it, v2.1.311.
In the changelogs
2Releases whose published page names CLAUDE_CODE_PLAIN_DELTA_FAST_PATH.
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v2.1.311
New opt-in shortcut for streaming plain text output
Setting CLAUDE_CODE_PLAIN_DELTA_FAST_PATH turns on a quicker way of passing along plain streamed text when Claude Code runs without its interactive screen
found in this entry's text, named in this entry
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v2.1.311
Headless runs report streamed text sent straight to output
Headless sessions now log how many streamed reply pieces went straight to output under
CLAUDE_CODE_PLAIN_DELTA_FAST_PATHfound in this entry's text, named in this entry
First cited
2The earliest release whose published evidence quoted CLAUDE_CODE_PLAIN_DELTA_FAST_PATH was v2.1.311, 26 Oct 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.
Presence across releases
1Build by build
2One 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 environment variable does. All environment variables.