What it is
A new env var lets session-start announcements be placed before the closing line in headless runs
Not Anthropic's. This is the line from the earliest changelog entry here that named it, v2.1.277.
Presence across releases
1Build by build
2One 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.
First cited
1The earliest release whose published evidence quoted CLAUDE_CODE_SESSION_START_ANNOUNCEMENTS_BEFORE_PROMPT was v2.1.277, 18 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 above.
Names beside it
Every environment variable in the inventory starting claude_code_session, up to twelve of them.
CLAUDE_CODE_SESSION_Two env vars let background dispatchers inherit your plan and rate tier without an API call. never mined
CLAUDE_CODE_SESSION_ACCESS_TOKENRemote settings can now supply many more environment variables, including auth tokens and home directory paths. v2.1.138
CLAUDE_CODE_SESSION_ATTENDEDA new CLAUDE_CODE_SESSION_ATTENDED environment variable tells child processes whether the parent session is interactive v2.1.269
CLAUDE_CODE_SESSION_IDSkills from your claude.ai account can load as a source, but only if you set the sync env var. v2.1.138
CLAUDE_CODE_SESSION_KINDYou get a one-time warning line if a query names a model Claude Code does not recognise. v2.1.138
CLAUDE_CODE_SESSION_LOGNo description from anybody. v2.1.138
CLAUDE_CODE_SESSION_NAMEA blank CLAUDE_CODE_SESSION_NAME now falls back to the directory-derived name. v2.1.138
CLAUDE_CODE_SESSION_ORIGINA new CLAUDE_CODE_SESSION_ORIGIN environment variable is read and passed through to spawned subsessions. v2.1.259
CLAUDE_CODE_SESSIONEND_HOOKS_TIMEOUT_MSNonsense values in retry, MCP output and hook timeout env vars now fall back to defaults. v2.1.138
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.