Anthropic schedules Claude Sonnet 4.5 retirement

Anthropic plans to retire Claude Sonnet 4.5 (claude-sonnet-4-5-20250929) from the Claude API on November 30, 2026. It recommends migrating to Claude Sonnet 5.5.

Models: Claude Sonnet 4.5 (2025-09-29)

Read on platform.claude.com

Source: Claude Developer Platform release notes, checked Sep 30, 2026. Summarized from the provider’s announcement.