Skip to main content
AI Choice Engine

Model comparison

GPT-5.6 Luna vs GPT-6 Sol

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 Luna

Budget

vs

OpenAI

GPT-6 Sol

Balanced

AI model capability comparison
SpecificationGPT-5.6 LunaGPT-6 Sol
ProviderOpenAIOpenAI
TierBudgetBalanced
Context window1.05M1.05M
Max output128K128K
Input / 1M tokensWinner: $0.20$2
Output / 1M tokensWinner: $1.20$10
WeightsClosedClosed
Parametersprevious-generation GPT-5.6 small tierGPT-6 mid-price tier
Reasoning levelsnone, low, medium, high, xhigh, maxnone, low, medium, high, xhigh, max
Modalitiestext, imagetext, image
API model idgpt-5.6-lunagpt-6-sol
ReleasedJuly 9, 2026September 22, 2026
Artificial Analysis Intelligence Index [max] (2026-09-26)37.3Winner: 47.5
SWE-bench Verified (2026-09-01)93Not verifiedUnverified
Terminal-Bench 2.1 (2026-07-09)84.7Not verifiedUnverified
LiveBench (2026-09-05)73.6Not verifiedUnverified
DeepSWE 1.1 [max] (2026-09-22)Not verifiedUnverified68.8
OSWorld 2.0 (offline) [xhigh] (2026-09-22)Not verifiedUnverified60.5
Terminal-Bench 4.0 [max] (2026-09-26)Not verifiedUnverified43.9

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

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

Pricing tiers

GPT-5.6 Luna: Launch list was $1/$6; cut to $0.20/$1.20 on 2026-07-30. Above 272K input the whole request bills 2x input / 1.5x output. Cached input $0.02/MTok; cache writes 1.25x input; batch $0.10/$0.60.

GPT-6 Sol: Replaces GPT-5.6 Sol at 50% of its $4/$20 promo price. Cached input $0.20/MTok; cache writes $2.50 (1.25x). Above 272K input the whole request bills $4/$15 ($0.40 cached). Batch/Flex $1/$5; Fast mode $4/$20. Knowledge cutoff Apr 20 2026. Launched in the API, ChatGPT Work and Codex the same day.

BudgetRecord checked September 26, 2026

GPT-5.6 Luna

GPT-5.6 Luna was OpenAI's cheapest GPT-5.6 tier; GPT-6 Luna replaced it on 2026-09-22 at half the price ($0.10/$0.50).

Best for

  • Classification
  • High-volume chat
  • Latency-sensitive pipelines

Watch out

Superseded by GPT-6 Luna, which costs half as much and matches it on the Artificial Analysis index; still served, not deprecated.

BalancedRecord checked September 26, 2026

GPT-6 Sol

GPT-6 Sol brings GPT-6 Astra's training advances to OpenAI's mid-priced tier — OpenAI claims roughly half GPT-5.6 Sol's factual-error rate at half its price, with a 1.05M-token context.

Best for

  • Default OpenAI production model
  • Agentic coding
  • Long-context knowledge work

Watch out

Brand-new (2026-09-22): the DeepSWE figure is vendor-reported and it is not yet on the independent boards; long prompts above 272K bill $4/$15 for the whole request.

When the cheaper one wins

GPT-5.6 Luna is cheaper on output at $1.20 per million tokens against $10 for GPT-6 Sol — about 8.3×. 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 picker

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 Luna · GPT-6 Sol

Common questions

GPT-5.6 Luna vs GPT-6 Sol

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

Is GPT-5.6 Luna or GPT-6 Sol cheaper for input?
GPT-5.6 Luna is cheaper at $0.20 per million input tokens, against $2 for GPT-6 Sol — roughly 10× 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 Luna has tiered pricing: Launch list was $1/$6; cut to $0.20/$1.20 on 2026-07-30. Above 272K input the whole request bills 2x input / 1.5x output. Cached input $0.02/MTok; cache writes 1.25x input; batch $0.10/$0.60. GPT-6 Sol has tiered pricing: Replaces GPT-5.6 Sol at 50% of its $4/$20 promo price. Cached input $0.20/MTok; cache writes $2.50 (1.25x). Above 272K input the whole request bills $4/$15 ($0.40 cached). Batch/Flex $1/$5; Fast mode $4/$20. Knowledge cutoff Apr 20 2026. Launched in the API, ChatGPT Work and Codex the same day.
Is GPT-5.6 Luna or GPT-6 Sol cheaper for output?
GPT-5.6 Luna is cheaper at $1.20 per million output tokens, against $10 for GPT-6 Sol — roughly 8.3× 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 Luna has tiered pricing: Launch list was $1/$6; cut to $0.20/$1.20 on 2026-07-30. Above 272K input the whole request bills 2x input / 1.5x output. Cached input $0.02/MTok; cache writes 1.25x input; batch $0.10/$0.60. GPT-6 Sol has tiered pricing: Replaces GPT-5.6 Sol at 50% of its $4/$20 promo price. Cached input $0.20/MTok; cache writes $2.50 (1.25x). Above 272K input the whole request bills $4/$15 ($0.40 cached). Batch/Flex $1/$5; Fast mode $4/$20. Knowledge cutoff Apr 20 2026. Launched in the API, ChatGPT Work and Codex the same day.
Which has the larger context window, GPT-5.6 Luna or GPT-6 Sol?
Both accept about 1.05M tokens of context, so document length will not decide between them.
Do GPT-5.6 Luna and GPT-6 Sol 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 Luna or GPT-6 Sol?
GPT-5.6 Luna is the budget tier and GPT-6 Sol 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 Luna costs $0.20 per 1M tokens versus $2 for GPT-6 Sol — a 10x difference at the headline tier.
  • Measured capability: GPT-6 Sol leads Artificial Analysis Intelligence Index 47.5 to 37.3 (measured 2026-09-26).
  • Positioning: GPT-5.6 Luna sits in the budget tier, GPT-6 Sol in the balanced tier — most production volume (classification, extraction, summarisation) does not need the pricier tier.
Run the model pickerEstimate stack costAll model comparisons

Choosing a harness rather than a model — Cursor, Copilot, Claude Code, Windsurf, or Lovable? Compare agentic harnesses · Latest releases.