A Claude Code environment variable, read out of the shipped bundle.
It was in the build from v2.1.138 and was gone by v2.1.212.
Nobody has written a line about this one. It is not in any of Anthropic's reference tables and no changelog entry here carries a description of it. It is in the build, which is the whole of what this page can claim.
First seen v2.1.138 9 May 2026
Last seen v2.1.211 15 Jul 2026, gone by v2.1.212
Builds59 / 149on this box, as of v2.1.308
Written about v2.1.138 first named in a changelog, 9 May 2026
v2.1.138in the build not in the build never minedv2.1.308
In the changelogs
1
Releases whose published page names CLAUDE_CODE_MID_CONVERSATION_SYSTEM.
The earliest release whose published evidence quoted CLAUDE_CODE_MID_CONVERSATION_SYSTEM was v2.1.138, 9 May 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.
ReleaseDateThe span that was quoted
v2.1.1389 May 2026(!If() && !process.env.CLAUDE_CODE_MID_CONVERSATION_SYSTEM)
v2.1.1389 May 2026CLAUDE_CODE_MID_CONVERSATION_SYSTEM
Presence across releases
4
BuildsHow manyDatesReading
v2.1.138 – v2.1.15315 builds9 May 2026 → 12 May 2026 ◆in the build
v2.1.212 – v2.1.30885 builds16 Jul 2026 → 22 Oct 2026 ○not in the build
Build by build
149
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.
