Anthropic Retiring 1M Context Beta for Claude Sonnet 4.5 and 4.0 — Migration to 4.6 Required April 30

Anthropic Platform Docs·low signal

Anthropic is shutting down the 1M token context window beta for Claude Sonnet 4.5 and Claude Sonnet 4 on April 30, 2026. After this date, the context-1m-2025-08-07 beta header will have no effect on these models. Developers must migrate to Claude Sonnet 4.6 or Claude Opus 4.6, which support 1M token context natively at standard pricing with no beta header required. Agent developers using long-context workflows on older Sonnet versions need to update their model specifications immediately.