Skip to content
ModelCap

Head-to-head comparison

Gemini 3.8 Flash vs GPT-5.6 Luna

Gemini 3.8 Flash (Google) and GPT-5.6 Luna (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 3 September 2026

As of 3 September 2026, Gemini 3.8 Flash holds the stronger ModelCap Index position (#11 vs #18); and GPT-5.6 Luna is 3.1× cheaper per output token ($1.20/1M vs $3.75/1M).

Which should you choose?

Choose Gemini 3.8 Flash if…

  • you want the stronger overall ModelCap Index position — #11 against #18 (76.4 vs 69.7 points).
  • AA Intelligence Index is your yardstick — 58.7 against 52.3.
  • AA Terminal-Bench 2.1 is your yardstick — 87.6% against 80.9%.
  • AA Humanity's Last Exam is your yardstick — 47.8% against 39.5%.
  • you want the more recently listed model — Gemini 3.8 Flash was listed 2 September 2026, GPT-5.6 Luna 9 July 2026.

Choose GPT-5.6 Luna if…

  • API cost matters — $1.20/1M output tokens against $3.75/1M, about 3.1× cheaper.
  • your workload is prompt-heavy — input tokens cost $0.20/1M against $0.75/1M.
  • you want provider choice — 3 listed API providers against 2.

Gemini 3.8 Flash vs GPT-5.6 Luna: specs, pricing and context

Specification comparison of Gemini 3.8 Flash and GPT-5.6 Luna
FieldGemini 3.8 FlashGoogleGPT-5.6 LunaOpenAI
ModelCap Index position#11#18
Index score76.469.7
EvidenceMeasuredMeasured
Input price / 1M tokens$0.75$0.20
Output price / 1M tokens$3.75$1.20
Context window1M tokens1M tokens
Max output tokens66K128K
API providers listed23
Weight accessAPI onlyAPI only
Input modalitiesText, Image, Video, File, AudioFile, Image, Text
First listed2 September 20269 July 2026
PublisherGoogleOpenAI

Evidence: 1 public benchmark observation across 1 board · 6 public benchmark observations across 6 boards. Prices are the lowest listed API offer per million tokens observed on the OpenRouter catalogue.

Benchmark scores: Gemini 3.8 Flash vs GPT-5.6 Luna

Public benchmark boards where Gemini 3.8 Flash or GPT-5.6 Luna has a published result
BoardGemini 3.8 FlashGPT-5.6 LunaLeads
Arena codingArena (LMArena)—14971489–1505X-HighOnly one result
LMArena AgentLMArena—2.1%0.9%–3.4%X-HighOnly one result
ARC-AGI-2ARC Prize Foundation—59.6%MaxOnly one result
ARC-AGI-3ARC Prize Foundation—0.2%MaxOnly one result
AA Intelligence IndexArtificial Analysis58.7intelligence-index52.3intelligence-indexGemini 3.8 Flash
AA Terminal-Bench 2.1Artificial Analysis87.6%terminal-bench-2.180.9%terminal-bench-2.1Gemini 3.8 Flash
AA Humanity's Last ExamArtificial Analysis47.8%humanitys-last-exam39.5%humanitys-last-examGemini 3.8 Flash
Terminal-Bench 4.0Terminal-Bench (Laude Institute)—17.3%14.4%–20.1%Codex · MaxOnly 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.

Gemini 3.8 Flash vs GPT-5.6 Luna: common questions

Is Gemini 3.8 Flash better than GPT-5.6 Luna?

Gemini 3.8 Flash ranks higher on the ModelCap Index as of 3 September 2026: #11 against #18. 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.

Is Gemini 3.8 Flash cheaper than GPT-5.6 Luna?

GPT-5.6 Luna is cheaper on output tokens: $1.20/1M against $3.75/1M. Input tokens are $0.75/1M for Gemini 3.8 Flash and $0.20/1M for GPT-5.6 Luna. Prices are the lowest listed API offer ModelCap observed, in USD per million tokens.

Which has the bigger context window, Gemini 3.8 Flash or GPT-5.6 Luna?

Both publish a 1M-token context window.

Which is better for coding, Gemini 3.8 Flash or GPT-5.6 Luna?

AA Terminal-Bench 2.1: Gemini 3.8 Flash 87.6%, GPT-5.6 Luna 80.9% — Gemini 3.8 Flash leads.

Are Gemini 3.8 Flash and GPT-5.6 Luna open-weight models?

Gemini 3.8 Flash: API only. GPT-5.6 Luna: 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 Gemini 3.8 Flash and GPT-5.6 Luna?

ModelCap currently lists 2 API providers for Gemini 3.8 Flash and 3 for GPT-5.6 Luna, from the OpenRouter catalogue snapshot the site serves; each model page lists the providers and their prices.

How current is this Gemini 3.8 Flash vs GPT-5.6 Luna comparison?

Every figure comes from the sealed ModelCap dataset published 3 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.

Explore further