Claude Fable 5 vs Gemini 3.8 Flash
Head-to-head technical comparison of intelligence, capabilities, and API pricing.
Which should you use?
Claude Fable 5 leads on the composite index by 2.9 points (96.4 vs 93.5).
Their Arena Elo differs by only 13 points, inside the confidence intervals the public board reports, so human preference does not separate them.
Cost is the sharper difference: Claude Fable 5 is 13.3x the input price of Gemini 3.8 Flash ($10 against $0.75 per 1M), so at volume the choice is usually decided by budget rather than benchmarks.
Pick Claude Fable 5 when
- Higher composite index — 96.4 against 93.5, a gap of 2.9 points.
- Stronger on MMLU-Pro: 95.6% against 93.2%.
Pick Gemini 3.8 Flash when
- Cheaper input tokens — $0.75 against $10 per 1M, so Claude Fable 5 costs 13.3x as much to feed.
- Better value per point of measured capability: $0.008 per index point against $0.104.
Value per point of measured capability, at list input pricing: Gemini 3.8 Flash $0.008 · Claude Fable 5 $0.104 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.