Claude Sonnet 5 vs Gemini 3.8 Flash
Head-to-head technical comparison of intelligence, capabilities, and API pricing.
Which should you use?
Claude Sonnet 5 leads on the composite index by 1.3 points (94.8 vs 93.5).
Cost is the sharper difference: Claude Sonnet 5 is 2.7x the input price of Gemini 3.8 Flash ($2 against $0.75 per 1M), so at volume the choice is usually decided by budget rather than benchmarks.
Pick Claude Sonnet 5 when
- Higher composite index — 94.8 against 93.5, a gap of 1.3 points.
- Stronger on MMLU-Pro: 94.6% against 93.2%.
Pick Gemini 3.8 Flash when
- Ahead on Arena Elo by 22 points (1494 vs 1472), which is outside the board's published confidence intervals.
- Cheaper input tokens — $0.75 against $2 per 1M, so Claude Sonnet 5 costs 2.7x as much to feed.
- Better value per point of measured capability: $0.008 per index point against $0.021.
Value per point of measured capability, at list input pricing: Gemini 3.8 Flash $0.008 · Claude Sonnet 5 $0.021 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.