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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_willow_tern

A Claude Code feature flag, read out of the shipped bundle. No mined inventory carries it: everything below comes from what this site has written about it.

What it is

A writing-style prompt block can be forced on with an environment variable; otherwise it stays off.

Not Anthropic's. This is the line from the earliest changelog entry here that named it, v2.1.247.

Presence across releases

The miner has never read a build containing this name. It is here because a changelog entry of ours names it, which is evidence that it existed and not evidence of which releases carried it. The inventory starts at v2.1.138 and everything older than that was never mined.

Gate readings

ReleaseResolvedThis accountAnonymousCompiled default
v2.1.247 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. v2.1.247A "Writing for the user" prompt block, off unless explicitly turned on

    A writing-style prompt block can be forced on with an environment variable; otherwise it stays off.

    gate cited by this entry

  2. v2.1.247A model-capability toggle, tengu_willow_tern

    A new toggle applies only to models advertising an opus 5 prompt bundle capability.

    named in this entry, 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_willow, up to twelve of them.

tengu_willow_crateOpening the diff panel records one event with your terminal width bucket. 2.1.228 tengu_willow_modeNo description from anybody. never mined tengu_willow_prismNo description from anybody. 2.1.138 tengu_willow_tern_appliedA writing-style prompt block can be forced on with an environment variable; otherwise it stays off. never mined

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.