A Claude Code environment variable, read out of the shipped bundle.
It has been in the build since v2.1.217, including the newest one read.
How many subagents can be running in one session before the Agent tool refuses to spawn another (default: 20). Accepts a positive whole number in plain digits; anything else is ignored, so the variable can adjust the cap but can't disable it. Requires Claude Code v2.1.217 or later
The earliest release whose published evidence quoted CLAUDE_CODE_MAX_CONCURRENT_SUBAGENTS was v2.1.284, 28 Sep 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
v2.1.28428 Sep 2026Concurrent subagent limit reached. You can run ${e} subagents at once. Do not retry. If the user wants more concurrent subagents, ask them to increase CLAUDE_CODE_MAX_CONCURRENT_SUBAGENTS.
Presence across releases
1
BuildsHow manyDatesReading
v2.1.217 – v2.1.30981 builds21 Jul 2026 → 22 Oct 2026 ◆in the build
Build by build
81
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.
