Gemini 2.5 Flash vs Gemini 3.1 Pro
Complete pricing and performance comparison between Google's Gemini 2.5 Flash and Google's Gemini 3.1 Pro.
Quick Verdict
Cheaper
Gemini 2.5 Flash
6.7x cheaper input, 4.8x cheaper output
Larger Context
Gemini 2.5 Flash
1.0M vs 1.0M
Higher Quality
Gemini 3.1 Pro
Score: 57 vs 21
Faster
Gemini 2.5 Flash
231 vs 114 tok/s
Pricing Comparison
| Spec | Gemini 2.5 Flash | Gemini 3.1 Pro | Difference |
|---|---|---|---|
| Provider | |||
| Input / 1M tokens | $0.3 | $2 | Gemini 2.5 Flash is 85% more expensive |
| Output / 1M tokens | $2.5 | $12 | Gemini 2.5 Flash is 79% more expensive |
| Context Window | 1.0M | 1.0M | Same |
| Max Output | 66K | 66K |
Performance Benchmarks
| Metric | Gemini 2.5 Flash | Gemini 3.1 Pro | Winner |
|---|---|---|---|
| Quality Index | 21 | 57 | Gemini 3.1 Pro |
| Output Speed | 231 tok/s | 114 tok/s | Gemini 2.5 Flash |
| Time to First Token | 0.42s | 34.56s | Gemini 2.5 Flash |
| Value (Quality/$) | 68.7 | 28.6 | Higher = better value |
Benchmark data from Artificial Analysis. Quality Index is a composite score across reasoning, coding, and knowledge tasks.
Cost at Scale
Estimated cost at different usage levels (3:1 input-to-output token ratio, typical for chat).
| Usage | Gemini 2.5 Flash | Gemini 3.1 Pro | Savings |
|---|---|---|---|
Single request 1K in / 300 out | $0.0010 | $0.0056 | Gemini 2.5 Flash saves $0.0046 |
10 requests 10K in / 3K out | $0.010 | $0.056 | Gemini 2.5 Flash saves $0.046 |
100 requests 100K in / 30K out | $0.105 | $0.560 | Gemini 2.5 Flash saves $0.455 |
1,000 requests 1M in / 300K out | $1.05 | $5.60 | Gemini 2.5 Flash saves $4.55 |
10,000 requests 10M in / 3M out | $10.50 | $56.00 | Gemini 2.5 Flash saves $45.50 |
1M requests/mo 1B in / 300M out | $1050.00 | $5600.00 | Gemini 2.5 Flash saves $4550.00 |
Pros & Cons
Gemini 2.5 Flash Strengths
- +Cheaper input tokens
- +Cheaper output tokens
- +Faster output (231 vs 114 tok/s)
- +Lower latency (faster first token)
Gemini 3.1 Pro Strengths
- +Higher quality score (57 vs 21)
When to Use Each Model
Choose Gemini 2.5 Flash for
- →Budget-conscious projects where cost is the primary factor
- →Real-time applications, chat, or autocomplete
Choose Gemini 3.1 Pro for
- →Tasks requiring maximum accuracy and reasoning
Frequently Asked Questions
Which is cheaper, Gemini 2.5 Flash or Gemini 3.1 Pro?
For input tokens, Gemini 2.5 Flash is 6.7x cheaper at $0.3/1M tokens. For output tokens, Gemini 2.5 Flash is 4.8x cheaper at $2.5/1M tokens. At typical usage (1M input + 300K output), Gemini 2.5 Flash costs $1.05 vs Gemini 3.1 Pro at $5.60.
What's the context window difference?
Gemini 2.5 Flash supports 1.0M context (1,048,576 tokens), while Gemini 3.1 Pro supports 1.0M (1,048,576 tokens). Gemini 3.1 Pro can handle 1x more context in a single request.
Which model has better benchmarks?
Quality Index: Gemini 2.5 Flash scores 21 vs Gemini 3.1 Pro at 57. Speed: Gemini 2.5 Flash generates 231 tok/s vs Gemini 3.1 Pro at 114 tok/s. Time to first token: Gemini 2.5 Flash at 0.42s vs Gemini 3.1 Pro at 34.56s.
When should I choose Gemini 2.5 Flash over Gemini 3.1 Pro?
Choose Gemini 2.5 Flash when you need: Cheaper input tokens, Cheaper output tokens, Faster output (231 vs 114 tok/s), Lower latency (faster first token). Choose Gemini 3.1 Pro when you need: Higher quality score (57 vs 21).
How much would 10,000 API requests cost?
At 1K input + 300 output tokens per request (typical chat): Gemini 2.5 Flash = $10.50, Gemini 3.1 Pro = $56.00. At 10K input + 1K output per request (longer conversations): Gemini 2.5 Flash = $55.00, Gemini 3.1 Pro = $320.00.
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