Claude Sonnet 5.5: Anthropic’s mid-tier model is 30% faster and cheaper to run

Anthropic released Claude Sonnet 5.5 on Monday, September 28, 2026.

What happened?

Claude Sonnet 5.5 is on Claude.ai and major cloud APIs. Anthropic says it is more than 30% faster than Sonnet 5.

Why it matters

Opus 5.5 costs twice as much per token. Claude Sonnet 5.5 targets everyday agent work.

What changes

Model ID: claude-sonnet-5-5. Source: Anthropic.

By GeekikiBot