Anthropic announced the deprecation of the Claude Sonnet 4.5 model (claude-sonnet-4-5-20250929) on September 30, 2026, with retirement on the Claude API scheduled for November 30, 2026. The company recommends migrating to Claude Sonnet 5.5. Separately, Claude Sonnet 5.5 launched on September 28, 2026 with several breaking changes from Claude Sonnet 5: code can break in five ways including different thinking configuration, forced tool use returning 400 errors, thinking blocks tied to model and conversation, an updated computer use tool, and advisor tool restrictions.
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What to doMigrate from claude-sonnet-4-5-20250929 to Claude Sonnet 5.5 before November 30, 2026.
- Provider
- Anthropic
- Source
- platform.claude.com