CLAUDE_CODE_PLAIN_DELTA_FAST_PATH

Updated October 31, 2026 by Alex Sorokoletov

CLAUDE_CODE_PLAIN_DELTA_FAST_PATH is a Claude Code environment variable: When set, enables a fast path for emitting plain text streaming deltas directly; the fast path is disabled when it is unset. Added in v2.1.311 and still present in v2.1.315. It is not in the official reference.

Status	Present in v2.1.315
Added	Added in v2.1.311
Category	Other
Official docs	Not listed

How to set it

For one session, export it in the shell that starts Claude Code:

export CLAUDE_CODE_PLAIN_DELTA_FAST_PATH=<value>
claude

To apply it to every session, add it to the env object of a settings file:

// ~/.claude/settings.json
{
  "env": {
    "CLAUDE_CODE_PLAIN_DELTA_FAST_PATH": "<value>"
  }
}

Related variables

CLAUDE_CODE_ARTIFACT_COMMENT_FAST_ACK: Enables a quick acknowledgement reply to artifact comments before the work is finished; defaults to off.
CLAUDE_CODE_ARTIFACT_COMMENT_FAST_ACK_FIXED: When fast acknowledgement of artifact comments is on, selects the fixed set of acknowledgement messages; defaults to off.
CLAUDE_CODE_ARTIFACT_PATH_PIN: Enables path pinning for artifacts, requiring files be read before they are replaced or removed; on by default.
CLAUDE_CODE_ATTACHMENTS_BY_PATH: When set, the attachment handler takes the by-path route instead of an upload mode, so attachments are referenced by their file path rather than having their contents uploaded.
CLAUDE_PTY_HOST_NO_STABLE_PATH: On macOS, set to 1 to skip resolving a stable executable path for the background PTY host and use the current executable path instead.
CLAUDE_CODE_MANAGED_SETTINGS_PATH
CLAUDE_CODE_POLICY_HELPER_PS1_PATH
CLAUDE_RUNNER_CHECKOUT_PATH

Frequently asked questions

What does CLAUDE_CODE_PLAIN_DELTA_FAST_PATH do?

When set, enables a fast path for emitting plain text streaming deltas directly; the fast path is disabled when it is unset.

Which Claude Code version has CLAUDE_CODE_PLAIN_DELTA_FAST_PATH?

Added in v2.1.311 and still present in v2.1.315.

How do I set CLAUDE_CODE_PLAIN_DELTA_FAST_PATH?

Export it before starting Claude Code (export CLAUDE_CODE_PLAIN_DELTA_FAST_PATH=value), or add it to the "env" object in ~/.claude/settings.json to apply it to every session.

All variables, searchable: Claude Code environment variables.