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DisclaimerUnofficial, and not affiliated with Anthropic. Nearly all of this is read straight out of what ships: npm bundles, captured prompts, published docs. Anthropic's own notes go in verbatim, marked as theirs. The rest is my reading, and every entry carries the strings behind it. If one looks wrong, vote it down and say why.

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Claude Code v2.1.221

Auto mode bash-first prompt variant

Not switched on
Useful3 Signal4
Auto Mode Notable not in their notes

Auto mode can be told to do file reads, searches and edits through Bash, but it's off by default.

A bash-first auto mode variant sits behind CLAUDE_CODE_THRIFTY_SONIC, defaulting off.

Feature flag
tengu_thrifty_sonic On for this account, and not off by default

The flag server returned on for the one account this site reads, and nothing in this release compiles it off by default. The compiled default is shown below, and says which it is when we cannot read one: a fifth of gates compile in a string or a number rather than on or off, and most published releases have no gate table behind them at all. No client can see what the server returns for your account.

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

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

CLAUDE_CODE_THRIFTY_SONIC
What

Auto mode can be told to route file reads, searches and edits through Bash instead of the dedicated tools, but the gate defaults to off.

Details
  • the auto-mode attachment carries bashFirst and steerOnly flags
  • bashFirst changes the injected reminder to prefer the Bash tool, and the exit reminder adds a line telling the model to resume using the dedicated tools
  • steerOnly produces a shortened exit message
  • gated on CLAUDE_CODE_THRIFTY_SONIC, otherwise the gate "tengu_thrifty_sonic" with fallback false, and requires the Bash and edit/search tools to be present
Evidence

Resume using the dedicated tools for file reads, searches, and edits.

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

Related

Other releases about the same thing. Found by shared names or similar wording; neither means one caused the other.

See this entry in the whole of v2.1.221 →