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GPT-5.6 Luna vs Gemini 3.5 Flash

The value tier where volume work actually runs: OpenAI's Luna against Gemini Flash.

Figures as of , read live from the model registry Zeplik bills against.

What the numbers say

Derived from the live registry Zeplik routes and bills against. Credits: 1 credit = $0.10, computed from the raw provider rate with a 1.20x margin.

Side by side

GPT-5.6 Luna

OpenAI

GPT-5.6 Luna is a fast, cost-efficient model in OpenAI's GPT-5.6 series.

Provider
OpenAI
Context window
1.1M tokens
Input price
2.4 credits / 1M tokens ($0.20 raw)
Output price
14.4 credits / 1M tokens ($1.20 raw)
Vision (image input)
Yes
Tool calling
Yes
Extended reasoning
No

Best for

  • Balanced everyday work: writing, questions, brainstorming and summarization
  • Very long documents and codebases: a 1.1M-token window fits entire books or repositories in one conversation
  • Working with images: screenshots, charts, photos and scanned documents alongside text
  • Tool use and agents: reliably calls functions, so it can search, run skills and drive workflows

Gemini 3.5 Flash

Google

Gemini 3.5 Flash is Google's high-efficiency multimodal model, bringing near-Pro level coding and reasoning at Flash-tier cost and speed.

Provider
Google
Context window
1.0M tokens
Input price
18.0 credits / 1M tokens ($1.50 raw)
Output price
108 credits / 1M tokens ($9.00 raw)
Vision (image input)
Yes
Tool calling
Yes
Extended reasoning
No

Best for

  • High-volume everyday tasks where speed and cost matter: summaries, drafts, quick questions
  • Very long documents and codebases: a 1.0M-token window fits entire books or repositories in one conversation
  • Working with images: screenshots, charts, photos and scanned documents alongside text
  • Tool use and agents: reliably calls functions, so it can search, run skills and drive workflows

Try both on Zeplik

The honest answer to most model debates is to run your own prompt on both. Zeplik puts GPT-5.6 Luna and Gemini 3.5 Flash in the same chat, so you can switch mid-conversation and compare answers on the work you actually do.

Pick a model and ask. Your prompt opens in the Zeplik app with that model selected.

Model to ask

Frequently asked questions

What is the difference between GPT-5.6 Luna and Gemini 3.5 Flash?
GPT-5.6 Luna is about 7.5x cheaper on output tokens (14.4 vs 108 credits per 1M). GPT-5.6 Luna is the newer release (July 2026 vs May 2026).
Is GPT-5.6 Luna or Gemini 3.5 Flash cheaper?
GPT-5.6 Luna is cheaper: 14.4 credits per million output tokens against 108. 1 credit = $0.10, computed from the raw provider rate with a 1.20x margin.
Which has the larger context window, GPT-5.6 Luna or Gemini 3.5 Flash?
GPT-5.6 Luna, at 1.1M tokens against 1.0M.
Can I use both GPT-5.6 Luna and Gemini 3.5 Flash on Zeplik?
Yes. Zeplik is a multi-model chat, so both sit behind one account and you can switch between them mid-conversation to compare answers on your own prompt.
Do GPT-5.6 Luna and Gemini 3.5 Flash need a paid plan?
One of the two is open to free accounts; the other needs a paid plan (Plus or above).

Related comparisons

GPT-5.6 Luna detailsGemini 3.5 Flash detailsAll comparisons

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