Gemini 3.1 Flash Lite or GPT-6 Luna: which to choose?

Side-by-side comparison

Criterion	Gemini 3.1 Flash Lite	GPT-6 Luna
Developer	Google DeepMind	OpenAI
Released	May 7, 2026	September 22, 2026
Capability index	64.3 / 100	80.3 / 100
Input price	$0.25	$0.10
Output price	$1.5	$0.50
Cost of a typical task	$0.008	$0.003
Context window	1,048,576 tokens	1,050,000 tokens
Maximum output	65,536 tokens	128,000 tokens
Reasoning mode	Yes	Yes
Tool calling	Yes	Yes
Accepted inputs	text, image, video, audio, PDF	text, image, PDF
Open weights	No	No
Knowledge cutoff	January 2025	May 18, 2026

Two models head to head

Gemini 3.1 Flash Lite and GPT-6 Luna are two budget models, built for high volumes at a low price, one from Google DeepMind, the other from OpenAI. Gemini 3.1 Flash Lite was released on May 7, 2026, GPT-6 Luna on September 22, 2026.

All figures below come from public sources checked on October 22, 2026: models.dev and OpenRouter for prices and capabilities, Epoch AI for scores.

What the benchmarks say

On our capability index, Gemini 3.1 Flash Lite scores 64.3 out of 100 and GPT-6 Luna 80.3. GPT-6 Luna leads by 16 points.

On the 3 benchmarks reported for both, Gemini 3.1 Flash Lite wins 0 times and GPT-6 Luna 3:

GPQA Diamond (PhD-level science questions): Gemini 3.1 Flash Lite 81.8%, GPT-6 Luna 90.5%
OTIS Mock AIME (competition mathematics problems): Gemini 3.1 Flash Lite 80%, GPT-6 Luna 98.9%
FrontierMath (very hard research-level mathematics): Gemini 3.1 Flash Lite 27.7%, GPT-6 Luna 78.9%

Budget

Gemini 3.1 Flash Lite costs $0.25 per million input tokens and $1.5 per million output tokens; GPT-6 Luna costs $0.10 and $0.50.

For a typical agent task (read 20,000 tokens, write 2,000), expect $0.008 with Gemini 3.1 Flash Lite versus $0.003 with GPT-6 Luna. GPT-6 Luna is 2.7 times cheaper, a gap that adds up quickly over 1,000 tasks: $5 difference.

Run the numbers with your own volumes in the agent cost calculator.

Features and limits

GPT-6 Luna reads more in one go: 1,050,000 tokens of context (roughly 1,575 pages), versus 1,048,576 for Gemini 3.1 Flash Lite.

Reasoning mode: Gemini 3.1 Flash Lite yes, GPT-6 Luna yes. Tool calling: Gemini 3.1 Flash Lite yes, GPT-6 Luna yes. Image input: Gemini 3.1 Flash Lite yes, GPT-6 Luna yes.

Neither publishes its weights: both are used through an API.

Knowledge cutoff: January 2025 for Gemini 3.1 Flash Lite, May 18, 2026 for GPT-6 Luna.

In short

Our reading of the data:

Choose GPT-6 Luna for a higher capability index, a lower cost and a more recent release.

This verdict relies on public figures; it does not replace a trial on your own tasks.

Frequently asked questions

Gemini 3.1 Flash Lite or GPT-6 Luna: which is better?

On our index (Epoch AI data), Gemini 3.1 Flash Lite scores 64.3 and GPT-6 Luna 80.3 out of 100. The best choice also depends on price and on your use case.

Which one is cheaper?

GPT-6 Luna. To read 20,000 tokens and write 2,000, expect $0.008 with Gemini 3.1 Flash Lite and $0.003 with GPT-6 Luna (prices as of October 22, 2026).

Which one has the larger context window?

GPT-6 Luna, with 1,050,000 tokens versus 1,048,576.

Can I run Gemini 3.1 Flash Lite or GPT-6 Luna on my own servers?

No: both are closed models, available through an API.