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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.

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Claude Code v2.1.51

Built-in Claude API / Agent SDK Skill [In Development]

What

A comprehensive built-in skill for helping users build LLM-powered applications with Claude, including code examples for Python, TypeScript, Java, Go, Ruby, C#, PHP, and cURL.

Status

Added as part of the skills system, contains full documentation for:

  • All current Claude models (Opus 4.6, Sonnet 4.6, Haiku 4.5)
  • Adaptive thinking, effort parameter, compaction
  • Tool use, streaming, batches, files API
  • Agent SDK patterns
  • Language-specific SDK examples including a new C# SDK section
Evidence

Large string literal beginning with "# Building LLM-Powered Applications with Claude" (search for "Building LLM-Powered Applications with Claude")

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

Related

Other releases about the same thing. Found by shared names or similar wording; neither means one caused the other.

See this entry in the whole of v2.1.51 →