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DisclaimerUnofficial, and not affiliated with Anthropic. Nearly all of this is read straight out of what ships: npm bundles, captured prompts, published docs. Anthropic's own notes go in verbatim, marked as theirs. The rest is my reading, and every entry carries the strings behind it. If one looks wrong, vote it down and say why.

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Claude Code v2.1.221

Sandbox prompt lists temp directories per mode

You'll notice
Useful2 Signal0
Sandbox

Sandbox instructions now hide or collapse temp directory paths depending on your platform and sandbox mode.

$TMPDIR
What

The sandbox system-prompt block substitutes $TMPDIR for the temp directories only on Windows or when the sandbox mode is something other than relaxed; otherwise the temp directories are filtered out of the listed write-allow paths entirely.

Details
  • Gate is the platform check plus the sandbox mode check, not a config flag.
  • Relaxed mode on non-Windows: temp paths simply do not appear in the write-allow list shown to the model.
  • Windows or non-relaxed: the paths collapse into the single $TMPDIR placeholder.
Evidence

$TMPDIR

Strings lifted out of the shipped bundle, so the claim above can be checked against them.

Related

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

See this entry in the whole of v2.1.221 →