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Reading a new release v2.1.251 Analysing changes · 2/5 Sorting the findings · 1/4 steps 470 findings $18.91 so far

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 v2.0.0

Claude Sonnet 4.5 Model

What: New default model claude-sonnet-4-5-20250929 with improved performance for daily coding tasks

How to use:

# Sonnet 4.5 is now the default - no changes needed
claude

# Or explicitly specify it
claude --model sonnet45

Details:

  • Available across all platforms (first-party API, Bedrock, Vertex AI)
  • Automatic migration from previous default models
  • Described as "Smartest model for daily use"
  • Supports 1M token context window variant: claude-sonnet-4-5[1m]
  • Evidence: U10 at line 367516, GM1() at line 368315, model detection logic at line 340617 in v2.0.0

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 v2.0.0 →