tengu_heron_tallow — New Feature Gate [Feature-Flagged]

What

A new feature flag tengu_heron_tallow is available. It can also be enabled via the CLAUDE_CODE_HERON_TALLOW environment variable or via managed settings.

Status

Feature-flagged (also overridable via CLAUDE_CODE_HERON_TALLOW env var)

Details

Ohd() returns true if Z.CLAUDE_CODE_HERON_TALLOW env var is truthy, the managed settings object has tengu_heron_tallow: true, or the feature flag is on via Ke()
Ohd() is called inside mks(), which generates the hint text appended to tool-not-found errors in the model context when a tool call cannot be routed to any registered tool
When Ohd() is true and the tool name resolves to an existing-but-not-enabled tool: the hint changes from "X exists but is not enabled in this context. Use one of the available tools instead." to "X is disabled for this session, in subagents as well as here."
When Ohd() is true and the tool is in the known-but-session-unavailable set (sat()): the hint changes from "X is not available in this context. Use one of the available tools instead." to "X is disabled for this session."
The change shifts the model's framing from "try a different tool" toward "this tool is a session-level prohibition", which may affect how the model responds to tool-call failures in restricted sessions

Evidence

Ohd() function (search for "CLAUDE_CODE_HERON_TALLOW") and its changed hint strings (search for "is disabled for this session, in subagents as well as here")

Strings lifted out of the shipped bundle, so the claim above can be checked against them.

Read from

Feature flag

tengu_heron_tallow Off in both readings

The flag server returned off for the account this site reads and for the anonymous baseline. A reading of off cannot rule out a rollout these two readings sit outside of.

This account: off · anonymous baseline: off · compiled default in v2.1.217: not a boolean we can read

These values were read against a different version of Claude Code, so treat them as the nearest reading available instead of one taken on this release.

Read once, for one account on one subscription tier, against v2.1.217. It isn't a statement about your account. What a flag value here can and cannot tell you

What has happened since

Flag reading moved 10 Sep 2026 The flag server now returns off for tengu_heron_tallow, read as this account. A reading is one sample. Claude Code evaluates its flags remotely, so no client sees the targeting rule behind a value and this says nothing about your account.

Flag reading moved 10 Sep 2026 The flag server now returns nothing at all, having stopped carrying it for tengu_heron_tallow, read as this account. A reading is one sample. Claude Code evaluates its flags remotely, so no client sees the targeting rule behind a value and this says nothing about your account.

See this across every release →

How sure we are

One source agreesOne thing we can check says the same as this entry.

The name it cites is new in this buildNew in this build: tengu_heron_tallow

See this entry in the whole of v2.1.217 →

The build it came inv2.1.217

21 Jul 2026 · 27 entries, this one is #25.

Either side of it

v2.1.216Older
v2.1.218Newer

Open the release →

Names in this entry

flagtengu_heron_tallow
Default false. 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. CLAUDE_CODE_HERON_TALLOW turns on the same wording.
envCLAUDE_CODE_HERON_TALLOW
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.

Is this right?