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Gemini 3.1 Pro vs Gemini 3 Flash: Which AI Model Should You Choose?

Pricing, context windows, latency, capabilities, and a one-line code switch — everything you need to pick the right model.

Google
Multimodal
vs
Google
Multimodal
Verdict

Choose Gemini 3 Flash for cost-sensitive workloads — it is roughly 4.0× cheaper on input tokens. Choose Gemini 3.1 Pro when you need its broader capabilities or stronger benchmarks.

Side-by-side specs

SpecGemini 3.1 ProGemini 3 Flash
ProviderGoogleGoogle
CategoryMultimodalMultimodal
Input cost / 1M tokens$2.40$0.60
Output cost / 1M tokens$14.40$3.60
Context window2.0M tokens1.0M tokens
Max output tokens65,53665,536
Avg. latency——
FeaturedYesYes
NewYesYes
Capabilities
text
image
audio
video
text
image
audio
video

Pricing example

A typical chat workload of 100,000 input tokens plus 50,000 output tokens.

Gemini 3.1 Pro
$0.96

100K in × $2.40 + 50K out × $14.40

Gemini 3 Flash
$0.24

100K in × $0.60 + 50K out × $3.60

For this workload, Gemini 3 Flash is cheaper than Gemini 3.1 Pro by $0.72 per request.

Switch in one line

Both models live behind Railwail's OpenAI-compatible endpoint. Replace the model string and you are done.

JavaScript / TypeScript
import OpenAI from "openai";

const client = new OpenAI({
  apiKey: process.env.RAILWAIL_API_KEY,
  baseURL: "https://railwail.com/v1",
});

// Before — using Gemini 3.1 Pro
let r = await client.chat.completions.create({
  model: "gemini-3.1-pro-preview",
  messages: [{ role: "user", content: "Hello" }],
});

// After — switched to Gemini 3 Flash
r = await client.chat.completions.create({
  model: "gemini-3-flash-preview",
  messages: [{ role: "user", content: "Hello" }],
});
Python
from openai import OpenAI

client = OpenAI(
    api_key=os.environ["RAILWAIL_API_KEY"],
    base_url="https://railwail.com/v1",
)

# Before — using Gemini 3.1 Pro
r = client.chat.completions.create(
    model="gemini-3.1-pro-preview",
    messages=[{"role": "user", "content": "Hello"}],
)

# After — switched to Gemini 3 Flash
r = client.chat.completions.create(
    model="gemini-3-flash-preview",
    messages=[{"role": "user", "content": "Hello"}],
)
cURL
# Before — using Gemini 3.1 Pro
curl https://railwail.com/v1/chat/completions \
  -H "Authorization: Bearer $RAILWAIL_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "gemini-3.1-pro-preview",
    "messages": [{"role": "user", "content": "Hello"}]
  }'

# After — switched to Gemini 3 Flash
curl https://railwail.com/v1/chat/completions \
  -H "Authorization: Bearer $RAILWAIL_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "gemini-3-flash-preview",
    "messages": [{"role": "user", "content": "Hello"}]
  }'

Which one wins for...

Quick verdicts derived from public specs. Always validate on your own workload.

Coding
Gemini 3.1 Pro

Higher coding category match or larger context wins.

Writing
Gemini 3.1 Pro

Bigger context window helps maintain long-form coherence.

Long documents
Gemini 3.1 Pro

The larger context window is the deciding factor.

Vision
Tie

Multimodal/vision support is required for image inputs.

Real-time chat
Tie

Lower average latency wins for interactive UX.

Cost-sensitive
Gemini 3 Flash

The model with the lower input-token price wins.

Frequently asked questions

Which is cheaper, Gemini 3.1 Pro or Gemini 3 Flash?
Gemini 3 Flash is cheaper. On a 100K input + 50K output example, Gemini 3 Flash costs about $0.24 versus $0.96 for Gemini 3.1 Pro — a saving of $0.72.
Which has more context, Gemini 3.1 Pro or Gemini 3 Flash?
Gemini 3.1 Pro has the larger context window at 2.0M tokens, compared to 1.0M tokens for Gemini 3 Flash.
Is Gemini 3.1 Pro better than Gemini 3 Flash for coding?
For coding-heavy workloads we lean toward Gemini 3.1 Pro on this comparison — it scores higher on the relevant heuristics (category, tags, or context window). Both models are usable for code via Railwail's OpenAI-compatible endpoint, so the safest path is to A/B test on your own prompts.
Can I use both Gemini 3.1 Pro and Gemini 3 Flash via Railwail?
Yes. Both Gemini 3.1 Pro and Gemini 3 Flash are accessible through a single Railwail API key and the OpenAI-compatible /v1/chat/completions endpoint. You only change the "model" parameter to switch between them — no SDK swap, no separate billing.
How do I switch from Gemini 3.1 Pro to Gemini 3 Flash?
Replace the model identifier "gemini-3.1-pro-preview" with "gemini-3-flash-preview" in your request payload. Everything else — API key, base URL, request shape — stays the same. See the code example on this page for the exact one-line change.

Try Gemini 3.1 Pro and Gemini 3 Flash side by side

One API key, one endpoint, both models. Start free — no credit card required.

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