Anthropic: Claude Sonnet 4 and Opus 4 Retiring on June 15

On April 14, Anthropic announced the deprecation of two key models from the Claude 4 family: Claude Sonnet 4 (claude-sonnet-4-20250514) and Claude Opus 4 (claude-opus-4-20250514). Both models will be fully removed from the Claude API on June 15, 2026.

What’s Changing

The original Claude 4 models, launched in May 2025, are being replaced by newer 4.6 versions that bring significant improvements in agentic tasks, coding, and long contexts. Specifically:

• Claude Sonnet 4 is replaced by Claude Sonnet 4.6 (launched February 17, 2026)
• Claude Opus 4 is replaced by Claude Opus 4.6 (launched February 5, 2026)

After June 15, all API calls to the old model IDs will return an error.

Why This Matters

Many development teams still use the original Claude 4 models in production. Migrating to version 4.6 brings advantages — native 1M token context without beta headers, improved agentic behavior, and new tools like context compaction — but requires testing as there are behavioral changes (e.g., Opus 4.6 does not support prefilling assistant messages).

What You Need to Do

1. Identify all API calls using claude-sonnet-4-20250514 or claude-opus-4-20250514
2. Replace model IDs with the corresponding 4.6 versions
3. Test thoroughly, as Opus 4.6 recommends adaptive thinking instead of manual
4. Migration deadline: June 15, 2026.