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.

Source

"The beta header now has no effect on these models, and requests exceeding the standard 200k-token context window return an error."

Claude Platform release notes (API)

Published Apr 30, 2026

Modelpeers tracks changes to AI agents and models, each from its source. Follow Claude Sonnet 4.5 to get a weekly email when it changes.