Claude Sonnet 4 changelog

Every change to Claude Sonnet 4 that Modelpeers has recorded, newest first, each with the source it came from. The record starts Sep 17, 2025.

All (4)Retiring (2)Breaking changes (1)Quality (1)

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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