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Sweep 22 Oct 2026 · 04:32Z Build v2.1.308 527 read Stable v2.1.308 Latest v2.1.308 Next v2.1.308 Feeds RSS JSON llms.txt llms-full.txt Unofficial
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Claude Code v2.1.221 ·

Auto mode can be told to do its work through Bash ("thrifty sonic")

Auto mode can be told to use Bash for reads and edits if you set the env var.

Nothing to try yet Notable No documentation found In Development
JSON All of v2.1.221
Nothing to try yetTier: how much it should matter to you
3Useful: my rating, 1 to 5
5Signal: worth watching, 1 to 5
Auto ModeArea: what it touches
In DevelopmentKind: in v2.1.221,
What probably matters to youSection of the release

CLAUDE_CODE_THRIFTY_SONIC makes auto mode prefer cat, grep and sed over the dedicated tools; off by default.

What

A new check decides whether auto mode gets a "bash first" instruction block telling the model to use Bash instead of the dedicated read and edit tools. It is off in this build unless the env var is set.

Details
  • When it fires, the auto-mode system reminder appends prose telling the model to "read files with cat, head, or sed -n, search with grep and find, and make file changes with sed, heredocs, or short scripts".
  • The auto-mode-exit reminder then says " Resume using the dedicated tools for file reads, searches, and edits."
  • The attachment carries a new bashFirst field, set only when the session has Bash plus the edit tools available and the check returns true.
  • Gate: CLAUDE_CODE_THRIFTY_SONIC wins if set, otherwise the remote gate tengu_thrifty_sonic, whose in-source fallback is false.
Evidence

tengu_thrifty_sonic

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

Read from
Names in the bundleCLAUDE_CODE_THRIFTY_SONIC
Feature flag
tengu_thrifty_sonic Off by default, switched on for this account

The shipped code defaults this off, and the flag server returned on for the one account this site reads on this version. That is the reading that makes the entry above worth a second look, and it still says nothing about your account.

This account: on · anonymous baseline: on · compiled default in v2.1.221: off

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 v2.1.221. 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 The flag server now returns on for tengu_thrifty_sonic, 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 The flag server now returns nothing at all, having stopped carrying it for tengu_thrifty_sonic, 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: CLAUDE_CODE_THRIFTY_SONIC

See this entry in the whole of v2.1.221 →

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