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Sweep 28 Aug 2026 · 16:06Z Build v2.1.251 479 read Stable v2.1.236 Latest v2.1.251 Next v2.1.251 Feeds RSS JSON llms.txt

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.

Reference / Environment variables

CLAUDE_CODE_EXTRA_METADATA

A Claude Code environment variable, read out of the shipped bundle. It has been in the build since v2.1.138, including the newest one read.

What it is

tk is now a reserved metadata name and stripped from your extra metadata or body.

Not Anthropic's. This is the line from the earliest changelog entry here that named it, v2.1.232.

Presence across releases

ReleasesReadingDeclared typeDefault
2.1.245 – 2.1.251 6 releases never mined — —
2.1.242 – 2.1.243 2 releases in the build — —
2.1.160 – 2.1.241 73 releases in the build str —
2.1.138 – 2.1.159 20 releases in the build — —

A row reading never mined is a release with no archived bundle behind it. Nothing was read out of it, so nothing here says whether the name was in it. A declared type or a default is only ever what that release's own bundle stated.

Changelog entries naming it

  1. v2.1.232Per-turn attribution key sent as tk, and tk is now a reserved metadata name

    tk is now a reserved metadata name and stripped from your extra metadata or body.

    named in this entry

Documentation pages

None of Anthropic's documentation pages this site has a copy of carries this name.

Names beside it

Every environment variable in the inventory starting claude_code_extra, up to twelve of them.

CLAUDE_CODE_EXTRA_BODYJSON object to merge into the top level of every API request body. Useful for passing provider-specific parameters that Claude Code doesn't expose directly. A value exported in your shell also applies to the [background sessions](/docs/en/agent-view) you dispatch with claude agents or --bg. Before v2.1.206, background sessions ignored a shell-exported value and used whatever copy the background supervisor process inherited 2.1.138

Read out of the published npm bundle release by release, and out of Anthropic's own documentation as this site captured it. Nothing on this page is a description anybody here wrote about what the environment variable does. All environment variables.