{"version":"2.1.311","anchor":"fast-path-for-plain-stream-deltas","canonical_anchor":"fast-path-for-plain-stream-deltas","heading":"New CLAUDE_CODE_PLAIN_DELTA_FAST_PATH setting for headless streaming","tier":"use","area":"SDK","scope":"individual","heads_up":false,"url":"https:\/\/changelogs.core-directive.com\/v\/2.1.311\/e\/fast-path-for-plain-stream-deltas","release_url":"https:\/\/changelogs.core-directive.com\/v\/2.1.311","markdown":"### New CLAUDE_CODE_PLAIN_DELTA_FAST_PATH setting for headless streaming\n\nNew environment variable `CLAUDE_CODE_PLAIN_DELTA_FAST_PATH` turns on a shortcut for streamed output in headless sessions\n\n**Unclear.** The value that turns it on and the exact cases where the shortcut applies are not known.\n\n**What**\n\nThere is a new environment variable, `CLAUDE_CODE_PLAIN_DELTA_FAST_PATH`. An environment variable is a named setting you give a program when you start it. It applies to headless sessions, meaning Claude Code runs without its interactive screen, for example in print mode or when another program drives it.\n\n- `CLAUDE_CODE_PLAIN_DELTA_FAST_PATH` turns on a shortcut, `plainDeltasNeedOnlyEmit`, in the part that runs headless turns. With it, plain streamed pieces of a reply (\"deltas\") go straight to output.\n\n- When the shortcut is in effect, the session logs how many streamed pieces went straight to output during the turn.\n\nThe code that reads the variable was not traced.\n\n**Why**\n\nIf you run Claude Code headless, there is a new opt-in switch that changes how streamed reply text reaches the output. The log line shows how often the shortcut was used in a turn.\n\n- Area: SDK\n- Names: `CLAUDE_CODE_PLAIN_DELTA_FAST_PATH`\n- Tier: Use it now\n- Useful: 5\/5\n- Signal: 3\/5\n- Scope: individual\n- Heads-up: no"}