Gemini 3.1 Pro Preview vs Gemini 3.8 Flash: price, scores, context

Side-by-side comparison

Criterion	Gemini 3.1 Pro Preview	Gemini 3.8 Flash
Developer	Google DeepMind	Google DeepMind
Released	February 19, 2026	September 2, 2026
Capability index	79.3 / 100	83.7 / 100
Input price	$2	$0.75
Output price	$12	$3.75
Cost of a typical task	$0.064	$0.023
Context window	1,048,576 tokens	1,048,576 tokens
Maximum output	65,536 tokens	65,536 tokens
Reasoning mode	Yes	Yes
Tool calling	Yes	Yes
Accepted inputs	text, image, video, audio, PDF	text, image, video, audio, PDF
Open weights	No	No
Knowledge cutoff	January 2025	Not disclosed

What are we comparing?

This comparison pits two mid-range models, balancing quality and cost against each other: Gemini 3.1 Pro Preview and Gemini 3.8 Flash, both built by Google DeepMind. The first dates from February 19, 2026, the second from September 2, 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.

Which one is more capable?

On our capability index, Gemini 3.1 Pro Preview scores 79.3 out of 100 and Gemini 3.8 Flash 83.7. Gemini 3.8 Flash leads by 4.4 points.

On the 5 benchmarks reported for both, Gemini 3.1 Pro Preview wins 1 time and Gemini 3.8 Flash 4:

GPQA Diamond (PhD-level science questions): Gemini 3.1 Pro Preview 94.4%, Gemini 3.8 Flash 95.4%
OTIS Mock AIME (competition mathematics problems): Gemini 3.1 Pro Preview 95.6%, Gemini 3.8 Flash 98.9%
FrontierMath (very hard research-level mathematics): Gemini 3.1 Pro Preview 59.6%, Gemini 3.8 Flash 68.4%
APEX-Agents (professional tasks carried out by an agent): Gemini 3.1 Pro Preview 35.1%, Gemini 3.8 Flash 64.3%
Humanity's Last Exam (multidisciplinary expert questions): Gemini 3.1 Pro Preview 46.4%, Gemini 3.8 Flash 44.5%

Pricing

Gemini 3.1 Pro Preview costs $2 per million input tokens and $12 per million output tokens; Gemini 3.8 Flash costs $0.75 and $3.75.

For a typical agent task (read 20,000 tokens, write 2,000), expect $0.064 with Gemini 3.1 Pro Preview versus $0.023 with Gemini 3.8 Flash. Gemini 3.8 Flash is 2.8 times cheaper, a gap that adds up quickly over 1,000 tasks: $41.5 difference.

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

Features and limits

Both models have the same context window: 1,048,576 tokens, roughly 1,573 pages.

Reasoning mode: Gemini 3.1 Pro Preview yes, Gemini 3.8 Flash yes. Tool calling: Gemini 3.1 Pro Preview yes, Gemini 3.8 Flash yes. Image input: Gemini 3.1 Pro Preview yes, Gemini 3.8 Flash yes.

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

In short

Our reading of the data:

Choose Gemini 3.8 Flash 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 Pro Preview or Gemini 3.8 Flash: which is better?

On our index (Epoch AI data), Gemini 3.1 Pro Preview scores 79.3 and Gemini 3.8 Flash 83.7 out of 100. The best choice also depends on price and on your use case.

Which one is cheaper?

Gemini 3.8 Flash. To read 20,000 tokens and write 2,000, expect $0.064 with Gemini 3.1 Pro Preview and $0.023 with Gemini 3.8 Flash (prices as of October 22, 2026).

Which one has the larger context window?

Neither: both accept 1,048,576 tokens.

Can I run Gemini 3.1 Pro Preview or Gemini 3.8 Flash on my own servers?

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

Gemini 3.1 Pro Preview or Gemini 3.8 Flash: which to choose?