Gemini 2.5 Flash vs Gemini 3.1 Pro Preview Custom Tools
A side-by-side comparison of two multimodal models — real specs, pricing, strengths and weaknesses, and a clear verdict on which to choose. Kept current by our agents.
Quick verdict: which should you choose?
Choose Gemini 2.5 Flash if you need
- ✓Need custom tool extensions for specialized multimodal workflows
- ✓Require strong cross-modal coherence on mixed inputs with very large contexts
- ✓Can tolerate preview-stage instability and higher per-token cost
- ✓Want flexible configuration beyond native modalities
Choose Gemini 3.1 Pro Preview Custom Tools if you need
- ✓Need fast output at 208.19 t/s with low cost of $2.5 per million tokens
- ✓Require broad native support across text, image, audio, and video
- ✓Prefer a production-ready model without additional tool setup
- ✓Value strong speed-capability balance on large contexts
Verdict
Gemini 2.5 Flash leads on measurable speed (208.19 t/s), price ($2.5/M vs $12/M), and known intelligence (20.6), while Gemini 3.1 Pro Preview Custom Tools offers custom-tool extensibility and marginally larger context. The preview model trades higher cost and potential instability for flexible tool integration that the Flash variant lacks. For most multimodal workloads prioritizing efficiency, Gemini 2.5 Flash is the clearer choice based on available data.
Gemini 2.5 Flash vs Gemini 3.1 Pro Preview Custom Tools: side by side
| Spec | Gemini 2.5 Flash | Gemini 3.1 Pro Preview Custom Tools | Winner |
|---|---|---|---|
| Intelligence | 20.6 | — | Tie |
| Output speed | 208 t/s | — | Tie |
| Output price | $2.50/1M | $12.00/1M | Gemini 2.5 Flash |
| Context | 1049K | 1049K | Tie |
| Params | — | — | Tie |
| Type | Proprietary | Proprietary | Tie |
| Provider | Tie |
Detailed analysis
Pricing
Winner: Gemini 2.5 FlashGemini 2.5 Flash costs $2.5 per million output tokens while Gemini 3.1 Pro Preview Custom Tools costs $12 per million. The fourfold price difference favors Flash for high-volume use. No other cost factors are provided.
Speed & Intelligence
Winner: Gemini 2.5 FlashGemini 2.5 Flash reports 208.19 tokens per second and an intelligence index of 20.6. Gemini 3.1 Pro Preview Custom Tools lists neither metric. Flash therefore demonstrates concrete performance advantages on the supplied data.
Context Handling
Winner: TieBoth models support roughly 1M-token contexts (1,048,756 vs 1,048,576). Gemini 3.1 Pro Preview Custom Tools emphasizes effective use of large windows and custom tools, while Gemini 2.5 Flash notes efficient handling but practical limits on full utilization.
Tooling & Extensibility
Winner: Gemini 3.1 Pro Preview Custom ToolsOnly Gemini 3.1 Pro Preview Custom Tools lists custom tools and flexible extension. Gemini 2.5 Flash provides no tooling features, making the preview model the sole option when custom capabilities are required.
Gemini 2.5 Flash
Pros
- +Broad native support for multiple input modalities
- +Efficient handling of very large contexts
- +Strong balance of speed and capability
- +Versatile across text, vision and audio tasks
Cons
- –Lower peak performance than larger Gemini variants on complex tasks
- –Speed optimizations may reduce depth on nuanced reasoning
- –Practical limits on full 1M-token context utilization
Gemini 3.1 Pro Preview Custom Tools
Pros
- +Strong cross-modal coherence on mixed inputs
- +Effective use of very large context windows
- +Flexible extension via custom tools
Cons
- –Preview status may include occasional instability
- –Large contexts can increase latency and cost
- –Tool setup requires additional configuration
Summary: Gemini 2.5 Flash vs Gemini 3.1 Pro Preview Custom Tools
Choose Gemini 2.5 Flash when speed, cost, and production stability matter most. Select Gemini 3.1 Pro Preview Custom Tools only when custom tools or specialized cross-modal coherence justify the higher price and preview limitations. The data support Flash for the majority of multimodal tasks.
Frequently asked questions
Gemini 2.5 Flash is faster, with a reported output speed of 208.19 tokens per second; no speed figure is given for Gemini 3.1 Pro Preview Custom Tools.