The 1M token context window beta (context-1m-2025-08-07) has been retired for Claude Sonnet 4.5 and Claude Sonnet 4. The beta header now has no effect on these models, and requests exceeding the standard 200k-token context window return an error. To use the 1M context window, migrate to Claude Sonnet 4.6 or Claude Opus 4.6, where it's generally available at standard pricing with no beta header required.
Fetched May 7, 2026