Claude Opus 5 vs Claude Sonnet 5
Head-to-head technical comparison of intelligence, capabilities, and API pricing.
Which should you use?
Claude Opus 5 leads on the composite index by 1.8 points (96.6 vs 94.8).
Cost is the sharper difference: Claude Opus 5 is 2.5x the input price of Claude Sonnet 5 ($5 against $2 per 1M), so at volume the choice is usually decided by budget rather than benchmarks.
Pick Claude Opus 5 when
- Higher composite index — 96.6 against 94.8, a gap of 1.8 points.
- Ahead on Arena Elo by 21 points (1493 vs 1472), which is outside the board's published confidence intervals.
- Stronger on MMLU-Pro: 95.7% against 94.6%.
Pick Claude Sonnet 5 when
- Cheaper input tokens — $2 against $5 per 1M, so Claude Opus 5 costs 2.5x as much to feed.
- Better value per point of measured capability: $0.021 per index point against $0.052.
Value per point of measured capability, at list input pricing: Claude Sonnet 5 $0.021 · Claude Opus 5 $0.052 per index point. Run your own token mix through the token cost calculator — a comparison at list price ignores caching and batch discounts, which move real bills more than this gap does.
Where these numbers come from
Figures as of 2026-09-07. Arena Elo and pricing are read from the public board and each vendor's own pricing page; see the full leaderboard for all 34 models and which columns are measured rather than estimated, or the benchmark matrix for scores benchmark by benchmark.