Head to head · October 2026

Gemini 3.1 Pro Preview vs Gemini 3.5 Flash API pricing

Gemini 3.5 Flash costs 1.3 times less per token at an 80/20 mix. Input costs 1.3x more on Gemini 3.1 Pro Preview. Output costs 1.3x more on Gemini 3.1 Pro Preview.

Google

Gemini 3.1 Pro Preview

Long context, multimodal input, document analysis.

Vendor: Google
Type: Frontier
SayGM in / out: $1.39 / $8.34
OpenRouter in / out: $2.11 / $12.66
Blended, 80/20: $2.780
Per 100M tokens: $278
Output share of bill: 60%
SayGM vs OpenRouter: 34% lower

Google

Gemini 3.5 Flash

Fast multimodal tasks, high-throughput apps.

Vendor: Google
Type: Frontier
SayGM in / out: $1.04 / $6.26
OpenRouter in / out: $1.58 / $9.50
Blended, 80/20: $2.084
Per 100M tokens: $208
Output share of bill: 60%
SayGM vs OpenRouter: 34% lower

§ 01

Monthly bill at three usage levels

Both models on SayGM. The bars show how the price ratio turns into dollars as volume grows.

Fig. 1Monthly bill at three usage levels

Gemini 3.1 Pro Preview on SayGM
Gemini 3.5 Flash on SayGM

Side project5M in · 1M out

$15

$11

Production app50M in · 15M out

$195

$146

High volume500M in · 100M out

$1,529

$1,146

Show data as a table

	Gemini 3.1 Pro Preview on SayGM	Gemini 3.5 Flash on SayGM
Side project (5M in · 1M out)	$15	$11
Production app (50M in · 15M out)	$195	$146
High volume (500M in · 100M out)	$1,529	$1,146

Usage is millions of input and output tokens per month. No caching discount applied. Source: published rate cards, October 2026 snapshot. Current prices on saygm.com.

§ 02

Verdict

A common pattern is to send routine requests to Gemini 3.5 Flash and escalate to Gemini 3.1 Pro Preview on failure or low confidence. On one key, that is a model name change per request rather than a second provider account.

§ 03

Per-token prices

OpenRouter figures include its 5.5% top-up fee.

USD per million tokens, input and output. OpenRouter includes its 5.5% top-up fee. Snapshot from October 2026.
Model	SayGMin / out	OpenRouterin / out, fee incl.	SayGM vs OpenRouter80/20 blend
Gemini 3.1 Pro PreviewGoogle	$1.39 / $8.34	$2.11 / $12.66	34% lower
Gemini 3.5 FlashGoogle	$1.04 / $6.26	$1.58 / $9.50	34% lower

Current SayGM rates

§ 04

Gemini 3.1 Pro Preview vs Gemini 3.5 Flash questions

Which is cheaper, Gemini 3.1 Pro Preview or Gemini 3.5 Flash?

Gemini 3.5 Flash is about 1.3 times cheaper than Gemini 3.1 Pro Preview at an 80/20 input to output mix on SayGM, as of October 2026.

How much do Gemini 3.1 Pro Preview and Gemini 3.5 Flash cost on OpenRouter?

Including the 5.5 percent top-up fee, Gemini 3.1 Pro Preview costs $2.11 input and $13 output per million tokens, and Gemini 3.5 Flash costs $1.58 and $9.50.

Can I use Gemini 3.1 Pro Preview and Gemini 3.5 Flash with one API key?

Yes. SayGM serves both through their native APIs on a single key, so simple tasks can go to Gemini 3.5 Flash and hard ones to Gemini 3.1 Pro Preview, or both can run in a cascade model.

§ 05