Claude Sonnet 4.5 changelog

Every change to Claude Sonnet 4.5 that Modelpeers has recorded, newest first, each with the source it came from. The record starts Apr 30, 2026.

All (2)Retiring (1)Breaking changes (1)

September 2026

Claude Sonnet 4.5

Model at Anthropic

RetiringSep 30, 2026

Claude Sonnet 4.5 deprecated, retiring November 30, 2026

Anthropic announced that claude-sonnet-4-5-20250929 will retire on the Claude API on November 30, 2026, with Claude Sonnet 5.5 as the recommended replacement.

Takes effect Nov 30, 2026 · in 29 days

Who is affected:: Apps calling claude-sonnet-4-5-20250929.
Action needed:: Migrate to claude-sonnet-5-5 before November 30, 2026.

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