As shipped in the CC 2.1.259 bundle, which differs from the open-source
copy in anthropics/skills (skills/claude-api/):
- model names/ids resolved (the bundle ships them as {{FABLE_NAME}}-style
catalog templates resolved at runtime; resolution verified byte-identical
against upstream for 54/69 files)
- includes the eval suite not yet published upstream: build-eval /
hillclimb subcommands in SKILL.md + shared/evals/ (build-eval,
eval-hillclimb, cost-hillclimb, eval-audit, report scaffolding)
- reviewer-only grounding comments stripped (as processSkillMarkdown does
at runtime; the model never sees them)
- SKILL.md frontmatter (name + description) taken verbatim from the live
skill registry
76 files: SKILL.md + shared/ + per-language dirs (python, typescript,
java, go, ruby, csharp, php, curl) + shared/evals/
Published on the docs page the same day as the model release. First
official prompt to carry the Mythos 5.1 / Fable 5.1 split, the visual
and designed-works reproduction rules with a worked example, and the
reply_after_tool_calls section.
- New skills/workflow-authoring/SKILL.md — the Workflow scripting reference (script API, resume, quality patterns, examples) moved out of the tool description into a skill
- Workflow tool description shrunk to opt-in rules + meta/pipeline example + "load the workflow-authoring skill"
- Artifact: CDN allowlist replaces the strict "self-contained only" CSP rule (cdnjs, jsdelivr, tailwind, jquery scripts; Google Fonts stylesheets); favicon required only on first publish; list shows favicon
- ListAgents wording tweak
- new Chrome browser automation section; placeholder style now [bracketed]
- Session context, Agents, and Skills nest under System prompt
- skill files gain frontmatter; add design-sync skill bundle
- one folder per skill (19 slash-menu + 2 internal), SKILL.md each
- starter-components/ holds verbatim sources for every copy_starter_component
kind; animations_v3 replaces v2
- system prompt reconciled against the live environment (ask_user, doc_page,
GitHub section, tool search)
- skills and starter-component listings link to the extracted files
First entry published on the docs page with zero lag (same day as model
release). Documents the Fable->Opus safeguards routing, Project
Glasswing / Claude Mythos Preview, and the June 12-30 export-control
suspension of Fable/Mythos.
