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Sweep 28 Aug 2026 · 00:00Z Build v2.1.250 478 read Stable v2.1.236 Latest v2.1.250 Next v2.1.250 Feeds RSS JSON llms.txt

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.

Reference / Feature flags

tengu_velvet_mallet

A Claude Code feature flag, read out of the shipped bundle. It was in the build from v2.1.166 and was gone by v2.1.196.

What it is

An alternate prompt wording for two tools exists but stays off unless you set an environment variable.

Not Anthropic's. This is the line from the earliest changelog entry here that named it, v2.1.223.

Presence across releases

ReleasesReadingDeclared typeDefault
2.1.245 – 2.1.250 5 releases never mined — —
2.1.196 – 2.1.243 47 releases not in the build — —
2.1.166 – 2.1.195 23 releases in the build — bool:false

A row reading never mined is a release with no archived bundle behind it. Nothing was read out of it, so nothing here says whether the name was in it. A declared type or a default is only ever what that release's own bundle stated.

Gate readings

ReleaseResolvedThis accountAnonymousCompiled default
v2.1.228 read on another version Off in both readings off off not a boolean we can read
v2.1.223 read on another version Off in both readings off off not a boolean we can read

Two arms, because they disagree: this account is the one account this site reads and anonymous is a baseline with no identity attached. A reading says nothing about your account, and off cannot rule out a rollout both readings sit outside of. What these readings can and cannot show.

Changelog entries naming it

  1. v2.1.228Write-before-Read rule is now decided locally, not by a remote flag

    Writing a file you have not read is now decided locally by model and permissions, not a server flag.

    gate cited by this entry

  2. v2.1.223New prompt-variant experiment for two tools

    An alternate prompt wording for two tools exists but stays off unless you set an environment variable.

    gate cited by this entry

Documentation pages

None of Anthropic's documentation pages this site has a copy of carries this name.

Names beside it

Every feature flag in the inventory starting tengu_velvet, up to twelve of them.

tengu_velvet_anchorNo description from anybody. never mined tengu_velvet_cascadeWhich models get the simple system prompt is now decided locally, not by remote config. 2.1.138 tengu_velvet_falcon_modelNo description from anybody. 2.1.163 tengu_velvet_hammerNo description from anybody. 2.1.166 tengu_velvet_harbor_owlA startup banner pitching Claude Enterprise to org admins exists but no one sees it by default. 2.1.238 tengu_velvet_ibisMAX_MCP_OUTPUT_TOKENS is still honoured first, but it's no longer sanity-checked as a number. 2.1.138 tengu_velvet_mothNo description from anybody. 2.1.138 tengu_velvet_staticNo description from anybody. 2.1.138 tengu_velvet_tideWhich models get the simple system prompt is now decided locally, not by remote config. 2.1.210

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 feature flag does. All feature flags.