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Google: Gemini 3.5 Flash vs Google: Gemini 3.1 Pro Preview Custom Tools: Complete Comparison 2026

Choosing between Google: Gemini 3.5 Flash and Google: Gemini 3.1 Pro Preview Custom Tools? We compare both tools across features, pricing, pros and cons to help you decide which is the better fit in 2026.

Google: Gemini 3.5 Flash9.2

Google · Video & Audio, Chatbots & LLMs

Gemini 3.5 Flash is Google's high-efficiency multimodal model, bringing near-Pro level coding and reasoning at Flash-tier cost and speed. It is highly optimized for coding proficiency and parallel agentic execution...

Google: Gemini 3.1 Pro Preview Custom Tools9.2

Google · Video & Audio, Chatbots & LLMs

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...

Key differences at a glance

  • •Both start at $1.50/1M tokens (Google: Gemini 3.5 Flash) and $2.00/1M tokens (Google: Gemini 3.1 Pro Preview Custom Tools).
  • •Context windows differ: Google: Gemini 3.5 Flash offers 1,048,576 tokens, Google: Gemini 3.1 Pro Preview Custom Tools offers 1,048,756 tokens.

Side-by-side comparison

FeatureGoogle: Gemini 3.5 FlashGoogleGoogle: Gemini 3.1 Pro Preview Custom ToolsGoogle
Quality score9.2 / 109.2 / 10
Starting price$1.50/1M tokens$2.00/1M tokens
Free tierNoNo
API input price$1.5 / 1M tokens$2 / 1M tokens
API output price$9 / 1M tokens$12 / 1M tokens
Speed——
Context window1,048,576 tokens1,048,756 tokens
CategoriesVideo & Audio, Chatbots & LLMsVideo & Audio, Chatbots & LLMs
Key features
  • 1,048,576-token context window
  • Vision (image input)
  • Reasoning / chain-of-thought
  • Tool / function calling
  • 1,048,756-token context window
  • Vision (image input)
  • Reasoning / chain-of-thought
  • Tool / function calling
Pros
      Cons

          Google: Gemini 3.5 Flash

          Choose Google: Gemini 3.5 Flash if you want content creation, research and writing.

          Google: Gemini 3.1 Pro Preview Custom Tools

          Choose Google: Gemini 3.1 Pro Preview Custom Tools if you want content creation, research and writing.

          Pricing comparison

          Google: Gemini 3.5 Flash
          $1.50/1M tokens
          API: $1.5 in / $9 out per 1M tokens
          Google: Gemini 3.1 Pro Preview Custom Tools
          $2.00/1M tokens
          API: $2 in / $12 out per 1M tokens

          The verdict

          Overall, Google: Gemini 3.5 Flash edges ahead with a quality score of 9.2 versus 9.2 for Google: Gemini 3.1 Pro Preview Custom Tools. Choose Google: Gemini 3.5 Flash if you want . That said, Google: Gemini 3.1 Pro Preview Custom Tools is the better pick when matters most — so the right answer depends on your priorities and budget.

          Try Google: Gemini 3.5 Flash →Try Google: Gemini 3.1 Pro Preview Custom Tools →

          Frequently asked questions

          Q. Which is better, Google: Gemini 3.5 Flash or Google: Gemini 3.1 Pro Preview Custom Tools?

          On our scoring, Google: Gemini 3.5 Flash edges ahead (9.2/10), but the right pick depends on your priorities and budget — see the breakdown above.

          Q. Is Google: Gemini 3.5 Flash or Google: Gemini 3.1 Pro Preview Custom Tools cheaper?

          Google: Gemini 3.5 Flash starts at $1.50/1M tokens and Google: Gemini 3.1 Pro Preview Custom Tools at $2.00/1M tokens. Check current rates before committing.

          Q. Can I use Google: Gemini 3.5 Flash and Google: Gemini 3.1 Pro Preview Custom Tools together?

          Yes — many teams use more than one AI tool, picking Google: Gemini 3.5 Flash for some tasks and Google: Gemini 3.1 Pro Preview Custom Tools for others where it's stronger.