Gemini 3.1 Pro Preview vs Gemini 3.8 Flash
Which one to choose
Pick Gemini 3.1 Pro when a task rewards Pro-tier reasoning: multi-step problems, debugging and planning where a wrong first answer is costly. Pick Gemini 3.8 Flash for long-horizon software engineering, autonomous agents and enterprise workflows on a stable, newer Flash model that Google recommends for new projects. Gemini 3.1 Pro is a preview that Google may change, so test both on your hardest prompts before committing.
Pricing comparison
| Gemini 3.1 Pro Preview | Gemini 3.8 Flash | |
|---|---|---|
| Model maker | ||
| Delivery availability | Available | Available |
| Context window | 1M | 1M |
| Max output | 64K | 64K |
| Official price | Input$2.00per 1M tokensOutput$12.00per 1M tokens | Input$0.75per 1M tokensOutput$3.75per 1M tokens |
| TokenLab price | Input$1.00per 1M tokensOutput$6.00per 1M tokens | Input$0.375per 1M tokensOutput$1.88per 1M tokens |
| Model performance |
|
|
| Capabilities | JSON modePrompt CacheTool useVision | JSON modePrompt CacheTool useVision |
Choose Gemini 3.1 Pro Preview when
- You solve hard multi-step problems where a wrong first answer is expensive
- You rely on Pro-tier reasoning for debugging and planning
- You analyse diagrams, charts or UI images together with text
Choose Gemini 3.8 Flash when
- You build autonomous agents or coding workflows that run for many steps
- You want the newest Gemini model Google recommends for new projects
- You need a model that is not tagged as a preview
How they differ
| Aspect | Gemini 3.1 Pro Preview | Gemini 3.8 Flash |
|---|---|---|
| Tier | Reasoning-first Pro model of the Gemini 3.1 line. | Google's most intelligent Flash model, in the newer 3.8 release. |
| Release status | Available as a preview; Google may change or retire it. | Released in September 2026 and recommended for new projects. |
| Focus | Complex problem solving and agentic coding with edit-and-test loops. | Long-horizon software engineering, autonomous agents and complex enterprise workflows. |
| Thinking | Built-in thinking before answering. | Thinking support for planning and debugging. |
| Shared surface | Text and images, tool calling, schema-bound JSON and caching. | Identical inputs and outputs, so the request format carries over. |
Summary
- Gemini 3.1 Pro Preview: Input $1.00 / Output $6.00 per 1M tokens; Gemini 3.8 Flash: Input $0.375 / Output $1.88 per 1M tokens. Rates depend on the billing unit, specification, and usage. Compare matching conditions in the model's detailed pricing; a single rate does not determine the total cost.
FAQ
Is Gemini 3.1 Pro better than Gemini 3.8 Flash?
Neither wins overall. Pro is the reasoning-first tier and may still do better on the hardest problems; 3.8 Flash is newer and aimed at long agent and coding runs. Test both on your hardest prompts.
Which model is newer?
Gemini 3.8 Flash is the newer model. It was released in September 2026 and Google recommends it for new projects, while Gemini 3.1 Pro is an earlier-generation model that is offered as a preview.
Can I swap one for the other without prompt changes?
The request format matches, since both take text and images, call tools and return schema-bound JSON. Behaviour differs, so run your evaluation set before switching.
Which is better for coding agents?
Gemini 3.8 Flash is positioned for long-horizon software engineering, so it is the first one to try for agents. Gemini 3.1 Pro also targets agentic coding with edit-and-test loops, and is worth testing on the hardest bugs.
Which is cheaper, Gemini 3.1 Pro Preview or Gemini 3.8 Flash?
Gemini 3.1 Pro Preview: Input $1.00 / Output $6.00 per 1M tokens; Gemini 3.8 Flash: Input $0.375 / Output $1.88 per 1M tokens. Rates depend on the billing unit, specification, and usage. Compare matching conditions in the model's detailed pricing; a single rate does not determine the total cost.
What are the key differences between Gemini 3.1 Pro Preview and Gemini 3.8 Flash?
Both models share similar capabilities.
Sources
Reviewed Oct 2, 2026