1M-token context window retired for Claude Sonnet 4.5/4 — migrate to Claude Sonnet 4.6 or Claude Opus 4.6

AI Impact Summary

The 1M token context window beta for Claude Sonnet 4.5 and Claude Sonnet 4 has been retired, removing the beta header and enforcing a hard 200k-token window. Any requests exceeding 200k tokens will error unless you migrate to the 4.6 lineage. Move to Claude Sonnet 4.6 or Claude Opus 4.6 to restore long-context capability, and update clients to use the new endpoints and versioning. This affects long-form processing pipelines (document ingestion, multi-pass summarization, long-context conversations) that relied on 1M-context windows.