Source Intelligence

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.

All of v2.1.251 Home All releases olderv2.1.250
Claude Code v2.1.251

Artifact publishing can attach page thumbnails, switched off in this build

Not switched on
Useful2 Signal4
Artifacts

Published pages could carry light and dark thumbnails, but the feature is off.

Thumbnail attachment on publish sits behind a remote flag defaulting false.

Feature flag
tengu_cobalt_plinth_campion Not enough to say

Nothing here resolved what this flag was doing on this version, so nothing here should be read as on or off.

This account: no value returned · anonymous baseline: no value returned · compiled default in v2.1.251: on

Read once, for one account on one subscription tier, against v2.1.251. It isn't a statement about your account. What a flag value here can and cannot tell you

What

Publishing a plain page can now scan it for declared thumbnail tags and attach a light and a dark thumbnail alongside the page. The whole path sits behind the remote config flag tengu_cobalt_plinth_campion, which defaults to false in this build, so no publish attaches thumbnails unless the server turns it on.

Details
  • Applies only to plain pages, not typed artifacts or live docs.
  • Sends thumbnail and thumbnailDark fields with the publish call.
  • Thumbnails that cannot be read are reported back as publish warnings rather than failing the publish.
  • Resolved thumbnail links are tracked in a per-publish cache.
Evidence

gatedThumbnailHrefs: new Map()

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

See this entry in the whole of v2.1.251 →