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AI Choice Engine

Model comparison

GPT-5.6 Terra vs GPT-6 Luna

Two OpenAI tiers compared on the figures that decide which one a workload actually needs.

Catalog record checked September 26, 2026Individual provider fields may changeEvidence confidence: High — see receipts below

OpenAI

GPT-5.6 Terra

Balanced

vs

OpenAI

GPT-6 Luna

Budget

AI model capability comparison
SpecificationGPT-5.6 TerraGPT-6 Luna
ProviderOpenAIOpenAI
TierBalancedBudget
Context window1.05M1.05M
Max output128K128K
Input / 1M tokens$2Winner: $0.10
Output / 1M tokens$12Winner: $0.50
WeightsClosedClosed
Parametersmid-tier reasoning modelGPT-6 low-cost tier
Reasoning levelsnone, low, medium, high, xhigh, maxnone, low, medium, high, xhigh, max
Modalitiestext, imagetext, image
API model idgpt-5.6-terragpt-6-luna
ReleasedJuly 9, 2026September 22, 2026
Artificial Analysis Intelligence Index [max] (2026-09-26)Winner: 42.137.3
SWE-bench Verified (2026-09-01)95.4Not verifiedUnverified
Terminal-Bench 2.1 (2026-07-09)87.4Not verifiedUnverified
LiveBench (2026-09-05)77.9Not verifiedUnverified
DeepSWE 1.1 [max] (2026-09-22)Not verifiedUnverified66.6

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

Where each score comes from, and how far it can be compared across models.

Pricing tiers

GPT-5.6 Terra: Launch list was $2.50/$15; cut to $2/$12 on 2026-07-30. Above 272K input the whole request bills 2x input / 1.5x output. Cached input $0.20/MTok; cache writes 1.25x input; batch $1/$6.

GPT-6 Luna: Direct successor to GPT-5.6 Luna at half the price. Cached input $0.01/MTok; cache writes $0.125. Above 272K input the whole request bills $0.20/$0.75 ($0.02 cached). Batch/Flex $0.05/$0.25; Fast mode $0.20/$1.00. Knowledge cutoff May 18 2026.

BalancedRecord checked September 26, 2026

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

GPT-6 Sol ($2/$10) now costs less than Terra ($2/$12) and scores higher — route frontier work to GPT-6 Sol. Terra has no named successor and is still served.

BudgetRecord checked September 26, 2026

GPT-6 Luna

GPT-6 Luna is OpenAI's cheapest current model at $0.10/$0.50 — the direct successor to GPT-5.6 Luna at half the price, with the full 1.05M-token context.

Best for

  • High-volume chat and extraction
  • Classification
  • Cost-capped agent loops

Watch out

Small tier: it matches GPT-5.6 Luna on the Artificial Analysis index but sits well below GPT-6 Sol on hard reasoning; the DeepSWE figure is vendor-reported at max effort.

When the cheaper one wins

GPT-6 Luna is cheaper on output at $0.50 per million tokens against $12 for GPT-5.6 Terra — about 24×. 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.

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Evidence 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.
  • 5/5 core specs verified on both sides — All core specifications verified for both models.
  • 1 shared named benchmark with differing scores — Measured on: Artificial Analysis Intelligence Index.
  • Verified within the last 90 days — Newest catalog check was 2 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.

Related comparisons

Diving deeper on one model? GPT-5.6 Terra · GPT-6 Luna

Common questions

GPT-5.6 Terra vs GPT-6 Luna

Answered from the verified figures on this page rather than general guidance.

Is GPT-5.6 Terra or GPT-6 Luna cheaper for input?
GPT-6 Luna is cheaper at $0.10 per million input tokens, against $2 for GPT-5.6 Terra — roughly 20× 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-5.6 Terra has tiered pricing: Launch list was $2.50/$15; cut to $2/$12 on 2026-07-30. Above 272K input the whole request bills 2x input / 1.5x output. Cached input $0.20/MTok; cache writes 1.25x input; batch $1/$6. GPT-6 Luna has tiered pricing: Direct successor to GPT-5.6 Luna at half the price. Cached input $0.01/MTok; cache writes $0.125. Above 272K input the whole request bills $0.20/$0.75 ($0.02 cached). Batch/Flex $0.05/$0.25; Fast mode $0.20/$1.00. Knowledge cutoff May 18 2026.
Is GPT-5.6 Terra or GPT-6 Luna cheaper for output?
GPT-6 Luna is cheaper at $0.50 per million output tokens, against $12 for GPT-5.6 Terra — roughly 24× 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-5.6 Terra has tiered pricing: Launch list was $2.50/$15; cut to $2/$12 on 2026-07-30. Above 272K input the whole request bills 2x input / 1.5x output. Cached input $0.20/MTok; cache writes 1.25x input; batch $1/$6. GPT-6 Luna has tiered pricing: Direct successor to GPT-5.6 Luna at half the price. Cached input $0.01/MTok; cache writes $0.125. Above 272K input the whole request bills $0.20/$0.75 ($0.02 cached). Batch/Flex $0.05/$0.25; Fast mode $0.20/$1.00. Knowledge cutoff May 18 2026.
Which has the larger context window, GPT-5.6 Terra or GPT-6 Luna?
Both accept about 1.05M tokens of context, so document length will not decide between them.
Do GPT-5.6 Terra and GPT-6 Luna 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-5.6 Terra or GPT-6 Luna?
GPT-5.6 Terra is the balanced tier and GPT-6 Luna the budget 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-6 Luna costs $0.10 per 1M tokens versus $2 for GPT-5.6 Terra — a 20x difference at the headline tier.
  • Measured capability: GPT-5.6 Terra leads Artificial Analysis Intelligence Index 42.1 to 37.3 (measured 2026-09-26).
  • Positioning: GPT-5.6 Terra sits in the balanced tier, GPT-6 Luna in the budget tier — most production volume (classification, extraction, summarisation) does not need the pricier tier.
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