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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.

← All of v2.1.239 Home All releases ←olderv2.1.238 v2.1.240newer→

Claude Code v2.1.239 21 Aug 2026

Two SDK fields drop their internal-only caveats

You'll notice

Useful2 Signal3

SDK

Two SDK fields dropped their internal-only caveats and now describe normal behaviour.

What

The source field on UserPromptSubmit no longer says it is set only for Anthropic-internal sessions during a trial; it now says payloads may omit it while the field rolls out. The setModel systemPrompt replacement no longer claims only the subprocess stdin transport honors it.

Details

setModel now states that transports which do not implement the replacement acknowledge success without applying it, so a success response is not proof the prompt changed.

Evidence

Payloads may omit it while the field rolls out.

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

See this entry in the whole of v2.1.239 →