What
A new environment variable, CLAUDE_CODE_PLAIN_DELTA_DIRECT_WRITE, changes how Claude Code sends streamed text when its output is read by another program. Deltas are the small pieces of a reply sent as it is written. Plain deltas are written out directly while the reading program is waiting for them, but only when all of these hold:
CLAUDE_CODE_PLAIN_DELTA_DIRECT_WRITEis set.CLAUDE_CODE_PLAIN_DELTA_FAST_PATHis also set.- The output format is
stream-json. - Verbose output is on.
Why
It is an opt-in way to cut delay for programs that read Claude Code's stream-json output.
Names in the bundleCLAUDE_CODE_PLAIN_DELTA_DIRECT_WRITE
One source agreesOne thing we can check says the same as this entry.
The name it cites is new in this build
New in this build: CLAUDE_CODE_PLAIN_DELTA_DIRECT_WRITE