Gemini 2.5 Flash Preview (Sep '25) (Reasoning) vs Gemini 3.1 Pro Preview: Which AI Model Is Better?

Updated March 26, 2026· Based on independent benchmark data

Quick Verdict

Gemini 3.1 Pro Preview leads in intelligence with a score of 57.2 vs 31.1. For speed, Gemini 3.1 Pro Preview wins at 113 tok/s vs 0 tok/s.

Head-to-Head Comparison

Metric	Gemini 2.5 Flash Preview (Sep '25) (Reasoning)	Gemini 3.1 Pro Preview
Intelligence Score	31.1	57.2
Coding Score	24.6	55.5
Math Score	78.3	N/A
Speed (tok/s)	0 tok/s	113 tok/s
Latency (TTFT)	0.00s	23.84s
Input Price / 1M tokens	Free	$2.00
Output Price / 1M tokens	Free	$12
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Detailed Analysis

Intelligence & Quality

Gemini 3.1 Pro Preview outperforms Gemini 2.5 Flash Preview (Sep '25) (Reasoning) on the intelligence index with a score of 57.2 compared to 31.1. For coding tasks, Gemini 3.1 Pro Preview has the edge with a coding score of 55.5 vs 24.6.

Speed & Latency

Gemini 3.1 Pro Preview generates output significantly faster at 113 tok/s compared to Gemini 2.5 Flash Preview (Sep '25) (Reasoning)'s 0 tok/s, making it Infinityx faster for streaming responses. Time to first token is 0.00s for Gemini 2.5 Flash Preview (Sep '25) (Reasoning) vs 23.84s for Gemini 3.1 Pro Preview, which affects perceived responsiveness in interactive applications.

Pricing

Gemini 2.5 Flash Preview (Sep '25) (Reasoning) is completely free, while Gemini 3.1 Pro Preview costs $2.00/1M input tokens and $12/1M output tokens.

Best Use Cases

Choose Gemini 3.1 Pro Preview when you need higher intelligence (57.2), stronger coding performance (55.5), faster output (113 tok/s).

Choose Gemini 2.5 Flash Preview (Sep '25) (Reasoning) if:

✓You want lower latency (0.00s vs 23.84s TTFT)
✓You want zero cost (Free vs paid)

Choose Gemini 3.1 Pro Preview if:

✓You need higher intelligence (score: 57.2 vs 31.1)
✓You prioritize coding performance (score: 55.5 vs 24.6)
✓You need faster throughput (113 tok/s vs 0 tok/s)
✓You need image understanding (Supports image input)

Frequently Asked Questions

Is Gemini 2.5 Flash Preview (Sep '25) (Reasoning) better than Gemini 3.1 Pro Preview for coding?

Gemini 3.1 Pro Preview scores higher on coding benchmarks (55.5 vs 24.6), making it the better choice for programming tasks.

Is Gemini 2.5 Flash Preview (Sep '25) (Reasoning) faster than Gemini 3.1 Pro Preview?

Gemini 3.1 Pro Preview is faster, producing output at 113 tok/s compared to Gemini 2.5 Flash Preview (Sep '25) (Reasoning)'s 0 tok/s.

Can Gemini 2.5 Flash Preview (Sep '25) (Reasoning) process images?

No, Gemini 2.5 Flash Preview (Sep '25) (Reasoning) does not support image input. However, Gemini 3.1 Pro Preview does support images.

Should I use Gemini 2.5 Flash Preview (Sep '25) (Reasoning) or Gemini 3.1 Pro Preview?

It depends on your priorities. Gemini 3.1 Pro Preview scores higher on intelligence (57.2), but Gemini 2.5 Flash Preview (Sep '25) (Reasoning) may be better for specific use cases like cost savings or speed-critical applications.

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View Gemini 2.5 Flash Preview (Sep '25) (Reasoning)details →View Gemini 3.1 Pro Previewdetails →Full pricing comparison →

Data last synced: March 26, 2026