Claude Sonnet 1M-token beta context window retired; migrate to Sonnet 4.6 or Opus 4.6

AI Impact Summary

The 1M-token context window beta for Claude Sonnet 4.x has been retired for Sonnet 4.5 and 4; requests exceeding 200k tokens will error. This removes the long-context option for workloads such as large documents, codebases, or multi-turn analyses previously relying on the beta. Migrate to Claude Sonnet 4.6 or Claude Opus 4.6, which are GA at standard pricing and require no beta header; ensure all clients target the new models and remove any beta-context headers. Validate large-context workloads in a test environment after migration and monitor for any changes in pricing or rate limits.