Claude Sonnet 4.5 Model / Claude Code v2.0.0

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

The build it came inv2.0.0

29 Sep 2025 · 31 entries, this one is #1.

Either side of it

Open the release →

Names in this entry

modelclaude-sonnet-4-5-20250929
The dated first-party API id of Sonnet 4.5 (claude-sonnet-4-5 in Claude Code's model table), also used for the anthropic_aws, anthropic_google_cloud and gateway providers. On the first-party provider, when certain account checks pass, a startup migration rewrites a user-settings model of claude-sonnet-4-5-20250929 or sonnet-4-5-20250929 (with or without [1m]) to sonnet or sonnet[1m].
modelclaude-sonnet-4-5
Writing a file you have not read is now decided locally by model and permissions, not a server flag.

Is this right?

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