New CLAUDE_CODE_NONBLOCKING_STDOUT env var for Ink renderer

A new env var stops Claude Code from hanging when stdout is slow, like when piped somewhere.

Use it now Notable New Features

JSON All of v2.1.261

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3Useful: my rating, 1 to 5

1Signal: worth watching, 1 to 5

Terminal RendererArea: what it touches

New FeaturesKind: in v2.1.261, 04 Sep 26

What probably matters to youSection of the release

A new CLAUDE_CODE_NONBLOCKING_STDOUT environment variable makes the terminal renderer install a non-blocking stdout writer with backpressure handling instead of writing directly. This can prevent the process from hanging when stdout is slow or blocked, such as when piped to a slow consumer.

Read from

Names in the bundleCLAUDE_CODE_NONBLOCKING_STDOUT

What the documentation says

Documented inclaude-code/env-vars

How sure we are

One source agreesOne thing we can check says the same as this entry.

The name it cites is new in this buildNew in this build: CLAUDE_CODE_NONBLOCKING_STDOUT

See this entry in the whole of v2.1.261 →

The build it came inv2.1.261

4 Sep 2026 · 179 entries, this one is #23.

Use it now15
You'll notice76
Nothing to try yet19
Under the hood69

Either side of it

v2.1.260Older
v2.1.263Newer

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Names in this entry

envCLAUDE_CODE_NONBLOCKING_STDOUT
Set to 1 to write terminal output through a second non-blocking file descriptor, so a terminal that stops reading, such as a paused tmux control-mode pane or a stalled SSH connection, can't freeze Claude Code mid-session. Applies on macOS, Linux, and WSL when stdout is a terminal. Requires Claude Code v2.1.261 or later

Is this right?

Other releases about the same thing. Found by shared names or similar wording; neither means one caused the other.

v2.1.267 Non-blocking stdout can now be enabled by a remote flag, not just an env var
Both mention nonblocking stdout