Claude Sonnet 5.5 vs Opus 5.5: Which to Use
Short Answer Default to Sonnet 5.5. It costs exactly half of Opus 5.5 on input and output ($2 / $10 vs $4 / $20 per million tokens), runs 30%+ faster than Sonnet 5, and lands within a few points of Opus 5.5 on most published benchmarks. Escalate to Opus 5.5 for complex, open-ended work that needs sustained judgment: architecture, long ambiguous investigations, anything where a wrong turn is expensive. Anthropic says Opus 5.5 “remains clearly stronger” there. Sonnet 5.5 was released on 28 September 2026. Model ID: claude-sonnet-5-5. Update, October 7, 2026 With the Claude Haiku 5.5 launch, Anthropic halved Sonnet 5.5 cache reads from $0.20 to $0.10 per million tokens, which it says makes Sonnet 5.5 about 20% cheaper on most agentic work. The table below is updated; the price chart shows the old rate. What Changed With Sonnet 5.5 Anthropic released Claude Sonnet 5.5 on 28 September 2026, six days after Opus 5.5 . It is available in the Claude apps, Claude Code, the Claude API, and on Amazon Web Services, Google Cloud and Microsoft Azure. Haiku 5.5 follows in the coming weeks. ...