tengu_cobalt_plinth_aspen
A Claude Code feature flag, read out of the shipped bundle. It has been in the build since v2.1.247, including the newest one read.
The preview browser is locked to the local server and refuses to run if the lock fails.
Not Anthropic's. This is the line from the earliest changelog entry here that named it, v2.1.247.
In the changelogs
7Releases whose published page names tengu_cobalt_plinth_aspen.
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v2.1.292
Emulator engine for artifact previews is built but cannot be selected yet
An emulator engine for artifact previews in remote sessions is built, but an internal switch that starts off keeps local Chrome in use
gate cited by this entry
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v2.1.283
Artifact preview turns itself off when no Chrome-type browser is found
Artifact preview now stays off when no Chrome, Chromium or Edge is found, unless
CLAUDE_CODE_ARTIFACT_PREVIEW=trueis setgate cited by this entry
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v2.1.283
Artifact preview is only offered when a local browser is found
The artifact preview action now needs a Chrome or Playwright browser found at startup, unless CLAUDE_CODE_ARTIFACT_PREVIEW is set to true
gate cited by this entry
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v2.1.280
Artifact verify/preview tools merged into a single 'check' tool
Artifact verify and preview tools are merged into one 'check' tool with old verb names still accepted
gate cited by this entry
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v2.1.257
New "check" artifact addon tool: local preview + runtime diagnostics, dark-launched behind two flags
A new check artifact addon previews a page locally and reads viewers' runtime diagnostics, behind two env vars.
found in this entry's text, gate cited by this entry
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v2.1.247
Preview locks the browser to the local server and self-tests the lock before loading
The preview browser is locked to the local server and refuses to run if the lock fails.
gate cited by this entry, found in this entry's text
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v2.1.247
Artifact
preview: a local headless-Chrome render check that is not compiled into this buildAn artifact preview action would screenshot a page locally at several widths, but it cannot run here.
gate cited by this entry, found in this entry's text
Gate readings
5| Release | Resolved | This account | Anonymous | Compiled default |
|---|---|---|---|---|
| v2.1.292 read on another version | Not enough to say | no value returned | no value returned | off |
| v2.1.283 read on another version | Not enough to say | no value returned | no value returned | off |
| v2.1.280 read on another version | Not enough to say | no value returned | no value returned | off |
| v2.1.257 read on another version | Not enough to say | no value returned | no value returned | off |
| v2.1.247 | Not enough to say | no value returned | no value returned | off |
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.
First cited
1The earliest release whose published evidence quoted tengu_cobalt_plinth_aspen was v2.1.247, 26 Aug 2026. That is the oldest release this project wrote about it, so it is a floor on the name's age and not the release that introduced it. It is not a presence reading: which builds carried the name is the table below.
Presence across releases
1Build by build
52One row per release since the first build this name was read out of. Absent means the build was read and the name was not in it, never mined means no bundle for that release was ever archived, and a declared type or a default is only ever what that release's own bundle stated.
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.