Gemini 3.1 Pro Preview vs Gemini 3.5 Flash
Too close to call on our weighted score (Gemini 3.5 Flash 69, Gemini 3.1 Pro Preview 68). The right pick depends on what you value most.
GoogleGemini 3.1 Pro Preview
68/100- ECI154.8
- Price$2.00 / $12.00
- Context1.05M
- Google
Gemini 3.5 Flash
69/100- ECI154.5
- Price$1.50 / $9.00
- Context1.05M
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Too close to call
It is close. Our weighted score puts them within 1 points (Gemini 3.5 Flash 69/100, Gemini 3.1 Pro Preview 68/100), so choose by what matters most for your work: Gemini 3.1 Pro Preview for raw capability and Gemini 3.5 Flash on price. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.
- CapabilityGemini 3.1 Pro PreviewCapabilities Index (ECI): Gemini 3.1 Pro Preview 154.8 · Gemini 3.5 Flash 154.5
- Lowest priceGemini 3.5 FlashGemini 3.5 Flash $3.38 · Gemini 3.1 Pro Preview $4.50 per 1M tokens (3:1 blend)
- Longest contextAbout the sameGemini 3.1 Pro Preview 1,048,576 · Gemini 3.5 Flash 1,048,576 tokens
- Widest inputsSame inputsGemini 3.1 Pro Preview: Text, Images, PDFs, Audio, Video · Gemini 3.5 Flash: Text, Images, PDFs, Audio, Video
- Self-hostingNo open weightsBoth are available only through APIs
| Measure | Weight | Gemini 3.1 Pro Preview | Gemini 3.5 Flash |
|---|---|---|---|
| CapabilityCapabilities Index (ECI) | 50% | 84 | 84 |
| Price | 25% | 19 | 25 |
| Inputs & features | 15% | 100 | 100 |
| Context window | 10% | 61 | 61 |
| Overall | 100% | 68/100 | 69/100 |
Every spec in one table
Highlighted cells lead their row. Dashes mean the data is not published.
| Specification | Gemini 3.1 Pro PreviewGoogle | Gemini 3.5 FlashGoogle |
|---|---|---|
| Capability | ||
| Capabilities Index (ECI) | 154.8 (best) | 154.5 |
| ECI rank | #31 of 148 (best) | #33 of 148 |
| GPQA DiamondGraduate-level science questions | 94.4% (best) | 92.8% |
| FrontierMath Tiers 1–3Research-level mathematics | 59.7% | 62.8% (best) |
| OTIS Mock AIME 2024–2025Competition mathematics | 95.6% (best) | 95.6% |
| SWE-bench VerifiedFixing real GitHub issues | 75.6% | 79.3% (best) |
| SimpleQA VerifiedShort factual questions | 73.5% (best) | 66.2% |
| Price per million tokens | ||
| Input | $2.00 | $1.50 (best) |
| Output | $12.00 | $9.00 (best) |
| Cached input | $0.20 | $0.15 (best) |
| Blended (3:1) | $4.50 | $3.38 (best) |
| Long-context rate | Over 200K: $4.00 / $18.00 | Same rate |
| Price source | Official Google API | Official Google API |
| Limits | ||
| Context window | 1,048,576 tokens | 1,048,576 tokens |
| Max output | 65,536 tokens | 65,536 tokens |
| Inputs and features | ||
| Text | Yes | Yes |
| Images | Yes | Yes |
| PDFs | Yes | Yes |
| Audio | Yes | Yes |
| Video | Yes | Yes |
| Reasoning | Yeslow · medium · high | Yesminimal · low · medium · high |
| Tool calling | Yes | Yes |
| Structured output | Yes | Yes |
| Availability | ||
| Weights | Proprietary | Proprietary |
| API model ID | gemini-3.1-pro-preview | gemini-3.5-flash |
| API providers | 26 | 32 (best) |
| Released | Feb 19, 2026 | May 19, 2026 |
| Knowledge cutoff | Jan 2025 | Jan 2025 |
What would a month cost?
Enter your expected volume in millions of tokens. List prices only; caching and batch discounts would lower these.
- Gemini 3.1 Pro Preview$44.00
- Gemini 3.5 Flash$33.00
Which should you choose?
Which is better: Gemini 3.1 Pro Preview or Gemini 3.5 Flash?
It is close. Our weighted score puts them within 1 points (Gemini 3.5 Flash 69/100, Gemini 3.1 Pro Preview 68/100), so choose by what matters most for your work: Gemini 3.1 Pro Preview for raw capability and Gemini 3.5 Flash on price. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.
Which is cheaper, Gemini 3.1 Pro Preview or Gemini 3.5 Flash?
Gemini 3.5 Flash is cheaper at $1.50 input / $9.00 output per million tokens (official Google API price). Gemini 3.1 Pro Preview costs $2.00 input / $12.00 output per million tokens (official Google API price). At a typical mix of three input tokens to one output token, that is $3.38 per million tokens for Gemini 3.5 Flash versus $4.50 for Gemini 3.1 Pro Preview (1.3× as much).
Which scores higher on benchmarks?
Gemini 3.1 Pro Preview scores higher on the Capabilities Index (ECI): Gemini 3.1 Pro Preview 154.8 (#31 of 148) and Gemini 3.5 Flash 154.5 (#33 of 148). The confidence ranges of the top two overlap (152.6–157.3 vs 152.5–156.6), so treat the gap as small. On individual benchmarks: GPQA Diamond — Gemini 3.1 Pro Preview 94.4%, Gemini 3.5 Flash 92.8%; FrontierMath Tiers 1–3 — Gemini 3.5 Flash 62.8%, Gemini 3.1 Pro Preview 59.7%; OTIS Mock AIME 2024–2025 — Gemini 3.1 Pro Preview 95.6%, Gemini 3.5 Flash 95.6%; SWE-bench Verified — Gemini 3.5 Flash 79.3%, Gemini 3.1 Pro Preview 75.6%; SimpleQA Verified — Gemini 3.1 Pro Preview 73.5%, Gemini 3.5 Flash 66.2%.
Which is better for coding?
Gemini 3.5 Flash resolves more real GitHub issues on SWE-bench Verified: Gemini 3.5 Flash 79.3% and Gemini 3.1 Pro Preview 75.6%. Both support tool calling for agent workflows.
Which has the bigger context window?
Gemini 3.1 Pro Preview and Gemini 3.5 Flash share the same 1,048,576-token context window. Maximum output per response: Gemini 3.1 Pro Preview up to 65,536, Gemini 3.5 Flash up to 65,536 tokens.
Which can read images, PDFs, audio or video?
Gemini 3.1 Pro Preview accepts text, images, PDFs, audio and video; Gemini 3.5 Flash accepts text, images, PDFs, audio and video. They handle the same number of input types.
Are any of these open source?
No. Gemini 3.1 Pro Preview and Gemini 3.5 Flash are proprietary and only available through APIs and apps.
Which is newer?
Gemini 3.5 Flash is the newest, released May 19, 2026. Gemini 3.1 Pro Preview came out Feb 19, 2026. Knowledge cutoff: Gemini 3.1 Pro Preview Jan 2025, Gemini 3.5 Flash Jan 2025.
How do you decide the winner?
Each model gets a 0–100 score on capability (50%, independent benchmark results); price (25%, blended price per million tokens (3 input : 1 output), log scale); inputs & features (15%, image, PDF, audio and video input, tool calling, structured output and reasoning); context window (10%, maximum tokens per request, log scale). Dimensions missing for any model are dropped and the remaining weights rescaled, so every model is judged on the same evidence. Specs and prices come from public model listings and the labs’ own API pages; capability scores come from independent benchmark runs. Data updated Oct 4, 2026.
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