CLAUDE_CODE_HERON_TALLOW
A Claude Code environment variable, read out of the shipped bundle. It was in the build from v2.1.217 and was gone by v2.1.229.
Boolean. Changes the hint added when the model calls a tool that is not available: for a known tool it reads <tool> is disabled for this session, in subagents as well as here. instead of exists but is not enabled in this context, and for Glob or Grep when Bash is also unavailable it reads <tool> is disabled for this session. The same wording is used when the tengu_heron_tallow flag is on.
Not Anthropic's. Written by Claude Opus 5.5 from reading the v2.1.228 bundle, and it can be wrong.
In the changelogs
1Releases whose published page names CLAUDE_CODE_HERON_TALLOW.
-
v2.1.217
tengu_heron_tallow— New Feature Gate [Feature-Flagged]found in this entry's text
First cited
1The earliest release whose published evidence quoted CLAUDE_CODE_HERON_TALLOW was v2.1.217, 21 Jul 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.
Presence across releases
2Build by build
80One 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.