GPT-5.6 Luna vs Claude Fable 5.1
Head-to-head technical comparison of intelligence, capabilities, and API pricing.
Which should you use?
Claude Fable 5.1 leads on the composite index by 4.9 points (92 vs 96.9).
Cost is the sharper difference: Claude Fable 5.1 is 50x the input price of GPT-5.6 Luna ($10 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 $10 per 1M, so Claude Fable 5.1 costs 50x as much to feed.
- Better value per point of measured capability: $0.002 per index point against $0.103.
Pick Claude Fable 5.1 when
- Higher composite index — 96.9 against 92, a gap of 4.9 points.
- Ahead on Arena Elo by 49 points (1504 vs 1455), which is outside the board's published confidence intervals.
- Stronger on MMLU-Pro: 95.9% against 92%.
Value per point of measured capability, at list input pricing: GPT-5.6 Luna $0.002 · Claude Fable 5.1 $0.103 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.
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