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Head-to-head comparison

GPT-5.5 vs GPT-5.6 Terra

GPT-5.5 (OpenAI) and GPT-5.6 Terra (OpenAI) compared on the ModelCap Index, API price, context window, provider availability, weight access and every public benchmark board they share. Figures are the same ones shown on the live rankings; nothing here is a hidden score.

Snapshot as of 22 September 2026

As of 22 September 2026, GPT-5.5 holds the stronger ModelCap Index position (#13 vs #21); and GPT-5.6 Terra is 2.5× cheaper per output token ($12.00/1M vs $30.00/1M).

Which should you choose?

Choose GPT-5.5 if…

  • you want the stronger overall ModelCap Index position — #13 against #21 (82.5 vs 79.7 points).
  • Arena coding is your yardstick — 1520 against 1518.
  • LMArena Agent is your yardstick — 5.0% against 1.4%.
  • ARC-AGI-2 is your yardstick — 85.0% against 83.9%.
  • AA τ²-Bench Telecom is your yardstick — 93.9% against 86.3%.
  • AA Humanity's Last Exam is your yardstick — 45.8% against 42.9%.

Choose GPT-5.6 Terra if…

  • API cost matters — $12.00/1M output tokens against $30.00/1M, about 2.5× cheaper.
  • your workload is prompt-heavy — input tokens cost $2.00/1M against $5.00/1M.
  • ARC-AGI-3 is your yardstick — 0.8% against 0.4%.
  • AA Intelligence Index is your yardstick — 42.1 against 38.4.
  • you want the more recently listed model — GPT-5.6 Terra was listed 9 July 2026, GPT-5.5 24 April 2026.

GPT-5.5 vs GPT-5.6 Terra: specs, pricing and context

Specification comparison of GPT-5.5 and GPT-5.6 Terra
FieldGPT-5.5OpenAIGPT-5.6 TerraOpenAI
ModelCap Index position#13#21
Index score82.579.7
EvidenceMeasuredMeasured
Input price / 1M tokens$5.00$2.00
Output price / 1M tokens$30.00$12.00
Context window1M tokens1M tokens
Max output tokens128K128K
API providers listed33
Weight accessAPI onlyAPI only
Input modalitiesFile, Image, TextFile, Image, Text
First listed24 April 20269 July 2026
PublisherOpenAIOpenAI

Evidence: 7 public benchmark observations across 7 boards · 6 public benchmark observations across 6 boards. Prices are the lowest listed API offer per million tokens observed on the OpenRouter catalogue.

Benchmark scores: GPT-5.5 vs GPT-5.6 Terra

Public benchmark boards where GPT-5.5 or GPT-5.6 Terra has a published result
BoardGPT-5.5GPT-5.6 TerraLeads
Arena codingArena (LMArena)15201514–1526High15181510–1525X-HighGPT-5.5
LMArena AgentLMArena5.0%4.1%–6.0%X-High1.4%0.3%–2.6%X-HighGPT-5.5
ARC-AGI-2ARC Prize Foundation85.0%X-High83.9%MaxGPT-5.5
ARC-AGI-3ARC Prize Foundation0.4%High0.8%MaxGPT-5.6 Terra
AA Intelligence IndexArtificial Analysis38.4intelligence-index:v4.3:xhigh42.1intelligence-index:v4.3:maxGPT-5.6 Terra
AA τ²-Bench TelecomArtificial Analysis93.9%tau2:telecom:dual-control:pass-at-1:3-repeats:source-model="GPT-5.5 (xhigh)":reasoning=true86.3%tau2:telecom:dual-control:pass-at-1:3-repeats:source-model="GPT-5.6 Terra (max)":reasoning=trueGPT-5.5
AA Humanity's Last ExamArtificial Analysis45.8%hle:may-2025:text-only-2158:no-tools:pass-at-1:source-model="GPT-5.5 (xhigh)":reasoning=true42.9%hle:may-2025:text-only-2158:no-tools:pass-at-1:source-model="GPT-5.6 Terra (max)":reasoning=trueGPT-5.5
Terminal-Bench 4.0Terminal-Bench (Laude Institute)—21.5%18.3%–24.8%Codex · MaxOnly one result
Terminal-Bench 2.1 Terminus 2Terminal-Bench78.0X-High—Only one result
WildClawBench OpenClawWildClawBench58.2—Only one result

Scores are the sources' own published figures for each model's best evaluated configuration; ModelCap never re-runs a benchmark.

Want a different pairing? Open the interactive comparison tool to swap either model for any current ranked language model.

GPT-5.5 vs GPT-5.6 Terra: common questions

Is GPT-5.5 better than GPT-5.6 Terra?

GPT-5.5 ranks higher on the ModelCap Index as of 22 September 2026: #13 against #21. That is a capability ranking built from public benchmark evidence with published uncertainty; whether it is "better" for you also depends on price, context and where you can run it. Their published uncertainty intervals overlap, so the rank difference alone does not establish a reliable capability advantage for your workload.

Is GPT-5.5 cheaper than GPT-5.6 Terra?

GPT-5.6 Terra is cheaper on output tokens: $12.00/1M against $30.00/1M. Input tokens are $5.00/1M for GPT-5.5 and $2.00/1M for GPT-5.6 Terra. Prices are the lowest listed API offer ModelCap observed, in USD per million tokens. For 1,000 requests with 2,000 input and 500 output tokens each (2M input + 0.5M output), the listed-rate estimate is $25.00 for GPT-5.5 versus $10.00 for GPT-5.6 Terra. GPT-5.6 Terra costs 60.0% less in this scenario. This excludes caching, batch discounts, prompt-length tiers, tool charges and retries; verify the selected endpoint before budgeting.

Which has the bigger context window, GPT-5.5 or GPT-5.6 Terra?

Both publish a 1M-token context window.

Which is better for coding, GPT-5.5 or GPT-5.6 Terra?

Arena coding: GPT-5.5 1520, GPT-5.6 Terra 1518 — GPT-5.5 leads.

Are GPT-5.5 and GPT-5.6 Terra open-weight models?

GPT-5.5: API only. GPT-5.6 Terra: API only. Open weights mean the checkpoint can be downloaded and self-hosted under its licence; API-only models are available solely through hosted endpoints.

Where can I run GPT-5.5 and GPT-5.6 Terra?

ModelCap currently lists 3 API providers for GPT-5.5 and 3 for GPT-5.6 Terra, from the OpenRouter catalogue snapshot the site serves; each model page lists the providers and their prices.

How current is this GPT-5.5 vs GPT-5.6 Terra comparison?

Every figure comes from the sealed ModelCap dataset published 22 September 2026; the page re-renders within a minute of each data refresh, and the ModelCap Index positions are the same ones shown on the live rankings.

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