Model comparison
GPT-5.5 Pro vs GPT-5.6 Terra
Two OpenAI tiers compared on the figures that decide which one a workload actually needs.
Catalog record checked September 3, 2026Individual provider fields may changeEvidence confidence: High — see receipts below
OpenAI
GPT-5.5 Pro
Frontier
OpenAI
GPT-5.6 Terra
Balanced
| Specification | GPT-5.5 Pro | GPT-5.6 Terra |
|---|---|---|
| Provider | OpenAI | OpenAI |
| Tier | Frontier | Balanced |
| Context window | 1.05M | 1.05M |
| Max output | 128K | 128K |
| Input / 1M tokens | $30 | Winner: $2 |
| Output / 1M tokens | $180 | Winner: $12 |
| Weights | Closed | Closed |
| Parameters | Not disclosedUnverified | mid-tier reasoning model |
| Reasoning levels | none, low, medium, high, xhigh, max | none, low, medium, high, xhigh, max |
| Modalities | text, image | text, image |
| API model id | gpt-5.5-pro | gpt-5.6-terra |
| Released | April 23, 2026 | July 9, 2026 |
| Artificial Analysis Intelligence Index [xhigh] (2026-08-14) | 60 | Not verifiedUnverified |
| Artificial Analysis Intelligence Index [high] (2026-08-14) | Not verifiedUnverified | 50 |
| SWE-bench Verified (2026-09-01) | Not verifiedUnverified | 95.4 |
| Terminal-Bench 2.1 (2026-07-09) | Not verifiedUnverified | 87.4 |
| LiveBench (2026-09-05) | Not verifiedUnverified | 77.9 |
Prices are USD per million tokens at standard rates, excluding batch and caching discounts. Bold indicates the better figure where one is objectively better. Values we could not confirm from the provider are shown as “Not verified” rather than estimated.
Benchmark receipts
- 2026-09-05: LiveBench official leaderboard (benchmark-owned), max effortContamination-resistant general capability across reasoning, coding, math, data analysis, and language, with monthly question refreshes. Comparability: comparable with caveat — Rolling question set: observations months apart measure different question mixes. Record the measurement date and compare within ~1 month windows.
- 2026-09-01: vals.ai SWE-bench Verified leaderboard (independent, mini-swe-agent bash-only) (independent; official SWE-bench not published)Real GitHub issue resolution: does the model's patch pass the hidden tests. Comparability: comparable with caveat — Post-audit vendor claims and pre-audit scores sit on different task trust levels; scaffolding (agent harness, compute budget) also dominates results. Never aggregate across scaffolds.
- 2026-08-14: Artificial AnalysisComposite index blending reasoning, knowledge, and coding evals into one 0–100 score. Comparability: directly comparable — AA occasionally rebaselines the index scale between snapshots — a score captured on one date is only comparable to same-snapshot scores (check measuredAt).
- 2026-07-09: OpenAI GPT-5.6 announcement (vendor; chart transcribed by Vellum)Agentic terminal work: multi-step tasks executed in a sandboxed shell environment. Comparability: comparable with caveat — Scores across Terminal-Bench major versions (v1 vs v2) are NOT comparable; harness configuration (container, time limits) also shifts results.
Pricing tiers: GPT-5.5 Pro: Standard $30/$180 per MTok; no cached-input discount. Batch $15/$90. · GPT-5.6 Terra: Launch list was $2.50/$15; cut to $2/$12 on 2026-07-30. Cached input $0.20/MTok; batch $1/$6.
GPT-5.5 Pro
GPT-5.5 Pro is OpenAI's highest-effort tier for maximal accuracy on the hardest tasks.
Best for
- Maximum-accuracy reasoning
- Research
- Hard enterprise workloads
Watch out
At $30/$180 per MTok it is the most expensive OpenAI tier; reserve for work that needs it.
GPT-5.6 Terra
GPT-5.6 Terra delivers roughly GPT-5.5-class quality at about half the cost, with the full 1.05M-token context.
Best for
- Cost-sensitive production
- Mixed reasoning workloads
- High-volume agents
Watch out
Quality trails Sol on the hardest tasks; route frontier work to Sol when it matters.
When the cheaper one wins
GPT-5.6 Terra is cheaper on output at $12 per million tokens against $180 for GPT-5.5 Pro — about 15×. Use the cheaper tier for classification, extraction, summarisation, and any task where the expensive model’s extra score does not change the accepted output. The expensive one only pays if your hardest task actually fails on the cheap tier. These are standard-tier API rates, excluding batch and cache discounts.
Run the model pickerEvidence confidence: High
How strong and complete the evidence behind this comparison is — not a prediction of which model is better.
- Pricing verified on both sides — Input and output rates are verified for both models.
- 4/5 core specs verified on both sides — Not published for at least one side: parameter count.
- 1 shared named benchmark with differing scores — Measured on: Artificial Analysis Intelligence Index.
- Verified within the last 90 days — Newest catalog check was 8 days ago.
- Both models carry source citations — Each side has at least two catalog sources on record.
Source receipts
Each catalog figure was checked against the provider or an independent second source on the date shown.
- GPT-5.5 Pro: OpenAI — Introducing GPT-5.5 (accessed 2026-08-29)
- GPT-5.5 Pro: OpenAI API pricing (gpt-5.5-pro $30/$180) (accessed 2026-08-29)
- GPT-5.6 Terra: OpenAI — GPT-5.6 (accessed 2026-08-29)
- GPT-5.6 Terra: OpenAI API pricing (gpt-5.6-terra $2/$12) (accessed 2026-08-29)
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- Claude Opus 5 vs GPT-5.5 Pro
- Claude Sonnet 5 vs GPT-5.6 Terra
Diving deeper on one model? GPT-5.5 Pro · GPT-5.6 Terra
Common questions
GPT-5.5 Pro vs GPT-5.6 Terra
Answered from the verified figures on this page rather than general guidance.
Is GPT-5.5 Pro or GPT-5.6 Terra cheaper for input?
GPT-5.6 Terra is cheaper at $2 per million input tokens, against $30 for GPT-5.5 Pro — roughly 15× the price. Output tokens usually dominate a real bill, so weigh the output rate more heavily than the input rate. These are base rates; GPT-5.5 Pro has tiered pricing: Standard $30/$180 per MTok; no cached-input discount. Batch $15/$90. GPT-5.6 Terra has tiered pricing: Launch list was $2.50/$15; cut to $2/$12 on 2026-07-30. Cached input $0.20/MTok; batch $1/$6.
Is GPT-5.5 Pro or GPT-5.6 Terra cheaper for output?
GPT-5.6 Terra is cheaper at $12 per million output tokens, against $180 for GPT-5.5 Pro — roughly 15× the price. Output tokens usually dominate a real bill, so weigh the output rate more heavily than the input rate. These are base rates; GPT-5.5 Pro has tiered pricing: Standard $30/$180 per MTok; no cached-input discount. Batch $15/$90. GPT-5.6 Terra has tiered pricing: Launch list was $2.50/$15; cut to $2/$12 on 2026-07-30. Cached input $0.20/MTok; batch $1/$6.
Which has the larger context window, GPT-5.5 Pro or GPT-5.6 Terra?
Both accept about 1.05M tokens of context, so document length will not decide between them.
Do GPT-5.5 Pro and GPT-5.6 Terra support the same reasoning levels?
Yes — both accept the same effort settings: "none", "low", "medium", "high", "xhigh", "max". Higher effort costs more and takes longer, so start low and raise it only where output quality actually improves.
Should I use GPT-5.5 Pro or GPT-5.6 Terra?
GPT-5.5 Pro is the frontier tier and GPT-5.6 Terra the balanced tier. The useful question is whether your hardest task actually fails on the cheaper one — most production volume such as classification, extraction and summarisation does not.
Next step
Choosing between them
The verified figures that separate this pair, computed from the catalog rather than restated boilerplate.
- Input price: GPT-5.6 Terra costs $2 per 1M tokens versus $30 for GPT-5.5 Pro — a 15x difference at the headline tier.
- Measured capability: GPT-5.5 Pro leads Artificial Analysis Intelligence Index 60 to 50 (measured 2026-08-14).
- Positioning: GPT-5.5 Pro sits in the frontier tier, GPT-5.6 Terra in the balanced tier — most production volume (classification, extraction, summarisation) does not need the pricier tier.
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