Fork Subagent Feature Gate [Gradual Rollout]

What

The /fork command's availability is additionally controlled by a server-side feature flag.

Status

Gated by tengu_copper_fox flag (defaults to !1), but can be overridden with CLAUDE_CODE_FORK_SUBAGENT environment variable.

Details

When the flag is disabled and the env var is not set, the fork tool is not loaded
Setting CLAUDE_CODE_FORK_SUBAGENT=1 provides a local override

Evidence

Fork feature gate (search for "tengu_copper_fox") — MG at line ~381717

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

Read from

Feature flag

tengu_copper_fox 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 v2.1.117: no gate table built for this version

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 v2.1.117. 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_copper_fox, 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_copper_fox, 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.

Anthropic's release notes agreeForked subagents can now be enabled on external builds by setting CLAUDE_CODE_FORK_SUBAGENT=1

See this entry in the whole of v2.1.117 →

The build it came inv2.1.117

21 Apr 2026 · 34 entries, this one is #33.

Either side of it

v2.1.116Older
v2.1.118Newer

Open the release →

Names in this entry

slash/fork
Copy the current conversation into a new background session and keep working here. Pass a prompt and the copy starts working on it immediately; without one it waits in agent view for its first prompt. Except when the copy edits in place, Claude Code instructs it to create a worktree of its own before making code changes; the isolation instruction requires Claude Code v2.1.221 or later. To hand a side task to a subagent whose result comes back into this conversation, use /subtask; to switch into a copy yourself, use /branch. Requires Claude Code v2.1.212 or later; on v2.1.161 through v2.1.211, and whenever agent view is turned off, /fork starts a forked subagent instead
flagtengu_copper_fox
Forked subagents are on by default in interactive sessions; set CLAUDE_CODE_FORK_SUBAGENT to false to opt out.
envCLAUDE_CODE_FORK_SUBAGENT
Controls fork mode, which lets Claude spawn forked subagents itself and is on by default in interactive sessions only. Set to 1 to turn it on in claude -p and the Agent SDK as well, or 0 to turn it off in every kind of session. You can run /subtask whether or not fork mode is on. The interactive default requires Claude Code v2.1.232 or later; on earlier versions, set the variable to 1 to turn fork mode on

Anthropic's note

Upstream's own release notes for v2.1.117 name something this entry names, so the two are probably about the same change. Probably: the pairing is made on a shared name rather than on the words around it.

Forked subagents can now be enabled on external builds by setting CLAUDE_CODE_FORK_SUBAGENT=1

Is this right?