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.

April 2026

Claude Sonnet 4.5 and Sonnet 4

2 models from Anthropic

Breaking changeApr 30, 2026

1M context beta retired for Sonnet 4.5 and Sonnet 4

The context-1m-2025-08-07 beta header stopped working for Claude Sonnet 4.5 and Sonnet 4, so requests over 200k tokens now fail.

Who is affected:: Apps sending more than 200k tokens to Sonnet 4.5 or Sonnet 4.
Action needed:: Move long-context work to Claude Sonnet 4.6 or newer.

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