CLAUDE_CODE_ATTRIBUTION_HEADER

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.

Releases whose published page names CLAUDE_CODE_ATTRIBUTION_HEADER.

1. v2.1.305 20 Oct 2026
   How Claude Code picks the claude.ai Project for usage reports

   The claude.ai Project used for usage reports now comes from an environment variable, a setting or a managed default, and bad IDs are flagged

   found in this entry's text

2. v2.1.302 16 Oct 2026
   Attribution block can name a project, and one fork subagent check no longer reads its variable

   The attribution block can now carry a project tag, and one fork subagent check now depends on remote sessions instead of CLAUDE_CODE_FORK_SUBAGENT

   found in this entry's text, named in this entry

3. v2.1.299 14 Oct 2026
   Managed settings can hold their CLAUDE_CODE_ATTRIBUTION_HEADER value against a host program

   Under some conditions, the managed-settings value of CLAUDE_CODE_ATTRIBUTION_HEADER now wins over one passed in by the program that starts Claude Code

   found in this entry's text, named in this entry

4. v2.1.284 28 Sep 2026
   Billing header now includes the prompt and turn position

   Requests sent directly to Anthropic now carry the prompt and turn number in their billing header, unless CLAUDE_CODE_ATTRIBUTION_HEADER turns it off

   found in this entry's text

5. v2.1.284 28 Sep 2026
   Attribution header can now include prompt and turn numbers

   On direct Anthropic connections, the attribution header can now also carry a prompt number and a turn number for each request

   found in this entry's text

6. v2.1.229 12 Aug 2026
   Attribution header can override the environment opt-out

   One first-party request path sends the attribution header even if you opted out via env var.

   named in this entry, found in this entry's text

7. v2.1.229 12 Aug 2026
   Auto-mode side queries always send the billing attribution header

   Auto-mode's side queries send billing attribution metadata even if you set the opt-out variable.

   named in this entry

8. v2.1.227 10 Aug 2026
   Billing attribution header carries a prompt id and validates its values

   Usage attribution headers can carry a prompt id, and one env var suppresses the header entirely.

   named in this entry, found in this entry's text

The earliest release whose published evidence quoted CLAUDE_CODE_ATTRIBUTION_HEADER was v2.1.299, 14 Oct 2026. That is the oldest release this project wrote about it, so it is a floor on the name's age and not the release that introduced it. It is not a presence reading: which builds carried the name is the table below.

One row per release since the first build this name was read out of. Absent means the build was read and the name was not in it, never mined means no bundle for that release was ever archived, and a declared type or a default is only ever what that release's own bundle stated.

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.