API cost decision in 10 seconds
Gemini 3.1 Pro Preview Custom Tools vs 🔥Gemini 3 Flash Preview
Pick Gemini 3 Flash Preview for lower cost; pick Gemini 3.1 Pro Preview Custom Tools only if the larger context window matters more.
Pricing data updated:
Prices normalized to USD per 1M tokens
Sample workload: 1M input + 500K output
Budget verdict
Pick Gemini 3 Flash Preview for lower cost; pick Gemini 3.1 Pro Preview Custom Tools only if the larger context window matters more.
On the standard 1M input plus 500K output workload, Gemini 3 Flash Preview is estimated at $2 vs $8 for Gemini 3.1 Pro Preview Custom Tools, saving $6 (75% lower).
Cost-first pickGemini 3 Flash Preview
Context-first pickGemini 3.1 Pro Preview Custom Tools
Sample savings$675%
10x traffic gap$60
Gemini 3.1 Pro Preview Custom Tools has more context, but Gemini 3 Flash Preview saves $6 on the standard workload. At 10x that traffic, the same price gap is about $60. Use the calculator below to replace the sample workload with your own token volume.
Cost sensitivity
Workload Sensitivity
Gemini 3 Flash Preview stays cheaper across input-heavy, balanced, and output-heavy sample workloads.
| Workload shape | Token mix | Better pick | Gemini 3.1 Pro Preview Custom Tools | Gemini 3 Flash Preview |
|---|---|---|---|---|
| Input-heavy / RAG | 5M input + 500K output | Gemini 3 Flash Preview | $16 | $4 |
| Balanced workload | 1M input + 1M output | Gemini 3 Flash Preview | $14 | $3.5 |
| Output-heavy chatbot | 1M input + 5M output | Gemini 3 Flash Preview | $62 | $15.5 |
Estimate your workload cost
Your Workload Cost
This estimate uses normalized public API pricing per 1M tokens. It is a planning aid, not a billing quote. Verify provider pricing, limits, and terms before production use.
Quick Decision
Gemini 3 Flash Preview has the lower input price, Gemini 3 Flash Preview has the lower output price, and Gemini 3.1 Pro Preview Custom Tools offers the larger context window.
For a 1M input token plus 500K output token workload, the estimated API cost is $8 for Gemini 3.1 Pro Preview Custom Tools and $2 for Gemini 3 Flash Preview.
Choose Gemini 3.1 Pro Preview Custom Tools when you care most about larger context window.
Choose Gemini 3 Flash Preview when you care most about lower input-token price, and lower output-token price.
| Feature | Gemini 3.1 Pro Preview Custom Tools (Google) | 🔥Gemini 3 Flash Preview (Google) |
|---|---|---|
| Input Price prompt tokens per 1M | $2 | $0.5 |
| Completion Price per 1M tokens | $12 | $3 |
| Sample Workload Cost 1M input + 500K output | $8 | $2 |
| Context Window | 1.05M | 1.05M |
| Release Date | 2026-02-25 | 2025-12-17 |
| Popularity | #7 |
Gemini 3.1 Pro Preview Custom Tools is a variant of Gemini 3.1 Pro that improves tool selection behavior by preventing overuse of a general bash tool when more efficient third-party...
Gemini 3 Flash Preview is a high speed, high value thinking model designed for agentic workflows, multi turn chat, and coding assistance. It delivers near Pro level reasoning and tool...
Use-Case Decision Matrix
| Use case | Better pick | Why |
|---|---|---|
| Budget-constrained production | Gemini 3 Flash Preview | On the standard 1M input plus 500K output workload, Gemini 3 Flash Preview is estimated at $2 vs $8 for Gemini 3.1 Pro Preview Custom Tools, saving $6 (75% lower). |
| High-volume input processing | Gemini 3 Flash Preview | Lower prompt-token price matters most when prompts or retrieved passages dominate the bill. |
| Long responses and chatbots | Gemini 3 Flash Preview | Lower output-token price matters most when assistants generate many completion tokens. |
| RAG or long-document work | Gemini 3.1 Pro Preview Custom Tools | A larger context window leaves more room for retrieved passages and source files. |