GPT-5.6 Terra vs GPT-5.5 Pro
Head-to-head technical comparison of intelligence, capabilities, and API pricing.
Which should you use?
GPT-5.6 Terra supersedes GPT-5.5 Pro in OpenAI's line-up, so this is an upgrade question rather than a bake-off.
GPT-5.6 Terra is also cheaper — $2 against $30 per 1M input tokens — so staying on GPT-5.5 Pro costs more for less.
Their Arena Elo differs by only 2 points, inside the confidence intervals the public board reports, so human preference does not separate them.
Cost is the sharper difference: GPT-5.5 Pro is 15x the input price of GPT-5.6 Terra ($30 against $2 per 1M), so at volume the choice is usually decided by budget rather than benchmarks.
Pick GPT-5.6 Terra when
- Cheaper input tokens — $2 against $30 per 1M, so GPT-5.5 Pro costs 15x as much to feed.
- Better value per point of measured capability: $0.021 per index point against $0.318.
Pick GPT-5.5 Pro when
- Stronger on MMLU-Pro: 94.2% against 93.5%.
Value per point of measured capability, at list input pricing: GPT-5.6 Terra $0.021 · GPT-5.5 Pro $0.318 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 2026-09-14. 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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