GPT-5.6 Luna vs Gemini 3.8 Flash
Head-to-head technical comparison of intelligence, capabilities, and API pricing.
Which should you use?
Gemini 3.8 Flash leads on the composite index by 1.5 points (92 vs 93.5).
Cost is the sharper difference: Gemini 3.8 Flash is 3.8x the input price of GPT-5.6 Luna ($0.75 against $0.2 per 1M), so at volume the choice is usually decided by budget rather than benchmarks.
Pick GPT-5.6 Luna when
- Cheaper input tokens — $0.2 against $0.75 per 1M, so Gemini 3.8 Flash costs 3.8x as much to feed.
- Better value per point of measured capability: $0.002 per index point against $0.008.
Pick Gemini 3.8 Flash when
- Higher composite index — 93.5 against 92, a gap of 1.5 points.
- Ahead on Arena Elo by 39 points (1494 vs 1455), which is outside the board's published confidence intervals.
- Stronger on MMLU-Pro: 93.2% against 92%.
Value per point of measured capability, at list input pricing: GPT-5.6 Luna $0.002 · Gemini 3.8 Flash $0.008 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.