Gemini 3.1 Pro vs Gemini 3.5 Flash: Thinking Levels, Parameters, and Official Specs

Choosing between Gemini models feels confusing.

Official documentation gives each a clear role.

Gemini 3.1 Pro targets deeper reasoning on complex tasks.

Gemini 3.5 Flash targets faster agentic workflows.

But there is a catch.

Without exact specs, picking the right one stays hard.

Here is the deal.

This guide pulls verified details straight from Google sources.

It covers thinking levels and parameters.

For Gemini 3.1 Pro vs Gemini 3.5 Flash.

You might be wondering how they line up.

In this guide, you'll see the official specs side by side.

Positioning Gemini 3.1 Pro for Complex Tasks

Gemini 3.1 Pro stands out as the model designed for advanced reasoning on the most complex tasks. Official documentation positions it as a smarter and more capable baseline that tackles problems requiring deeper intelligence rather than quick answers.

Official documentation describes it as a smarter, more capable baseline for complex problem-solving.

It focuses on tasks where a simple answer isn’t enough.

This approach applies advanced reasoning to your hardest challenges.

The model represents a step forward in core reasoning.

Gemini 3.1 Pro works best for complex tasks and bringing creative concepts to life.

Positioning Gemini 3.5 Flash for Agentic Speed

Gemini 3.5 Flash serves as the optimized choice for agentic speed in multi-step workflows. Official documentation positions it for sustained frontier-level intelligence at higher speed and lower cost, targeting real-world tasks at scale through sub-agent deployment and long-horizon planning.

Official documentation describes Gemini 3.5 Flash as designed for the agentic era.

It excels at sub-agent deployment.

The model supports multi-step workflows.

It handles long-horizon tasks at scale.

This positioning suits rapid agentic loops.

Such loops involve complex coding cycles and iterations.

Gemini 3.5 Flash delivers strong agentic capabilities at substantial speed and value.

Token Limits and Context Windows

Gemini 3.1 Pro and Gemini 3.5 Flash share an input token limit of 1,048,576 tokens. Official documentation shows an output limit of 65,536 for Gemini 3.1 Pro and 65,536 or 65,535 default for Gemini 3.5 Flash. These exact parameters come from verified Google sources.

Gemini 3.1 Pro lists a maximum input of 1,048,576 tokens.

It supports a maximum output of 65,536 tokens.

Gemini 3.5 Flash uses the same input limit of 1,048,576 tokens.

Its output limit reaches 65,536 according to API documentation.

Cloud documentation sets the default at 65,535 for output.

The input capacity stays identical across both models.

This allows equivalent handling of large context in prompts.

Output limits differ only slightly in reported defaults.

All figures reflect original data from official documentation.

Thinking Levels and Reasoning Modes

Original data from official documentation lists thinking levels for both Gemini 3.1 Pro and Gemini 3.5 Flash. Gemini 3.1 Pro uses the Thinking (High) designation in benchmark tables, while no explicit definitions of these levels are available.

Gemini 3.1 Pro Thinking Levels

Original documentation from Google sources applies the Thinking (High) label to Gemini 3.1 Pro.

This occurs in benchmark comparison tables.

The model also has Thinking listed among its supported capabilities.

No further details on the thinking levels are described.

Gemini 3.5 Flash Thinking Levels

Original documentation from Google sources lists Thinking as a supported capability for Gemini 3.5 Flash.

Benchmark tables reference this model without a specific level qualifier such as High.

No operational descriptions of the thinking levels appear in the materials.

Multimodal Inputs and Media Support

Gemini 3.1 Pro and Gemini 3.5 Flash both accept text, image, video, audio, and PDF inputs while generating text outputs. Official documentation confirms these shared multimodal capabilities for the two models without variation in core input types.

Gemini 3.1 Pro supports a maximum of 3000 images per prompt.

Video inputs reach approximately 45 minutes with audio.

Video lengths extend to approximately 1 hour without audio.

The model allows a maximum of 10 videos per prompt.

Audio inputs support approximately 8.4 hours per prompt.

Image file sizes stay at 7 MB for inline data or direct uploads.

Files from Google Cloud Storage reach up to 30 MB.

Gemini 3.5 Flash lists the same core input types of text, images, audio, video, and PDF.

Specific media length and file size constraints appear less detailed for Gemini 3.5 Flash in the available official sources.

Tool Integration and Agentic Capabilities

Gemini 3.1 Pro and Gemini 3.5 Flash both include function calling, code execution, structured outputs, and grounding features in their official specifications. Gemini 3.5 Flash stands out with explicit design for the agentic era through support for sub-agent deployment and multi-step workflows.

Official documentation lists function calling as supported for both models.

This feature enables connections to external tools and functions.

Code execution appears among the supported capabilities for Gemini 3.1 Pro and Gemini 3.5 Flash.

Structured outputs receive support in the documented feature lists for each model.

Grounding shows up with minor naming variations across sources.

Gemini 3.1 Pro includes grounding with Google Search.

Gemini 3.5 Flash lists search grounding.

Gemini 3.5 Flash documentation describes the model as designed for the agentic era.

It excels at sub-agent deployment and multi-step workflows.

Gemini 3.5 Flash also supports batch API, caching, file search, flex inference, and priority inference.

Gemini 3.1 Pro lists system instructions, count tokens, implicit context caching, and explicit context caching.

Gemini 3.1 Pro vs Gemini 3.5 Flash: Decision Framework

Gemini 3.1 Pro vs Gemini 3.5 Flash decisions hinge on matching task needs to Thinking (High) versus standard Thinking support along with shared 1,048,576 input token limits and near-identical 65,536 output parameters from official documentation.

Original data from official documentation provides the basis for this framework.

Gemini 3.1 Pro features the Thinking (High) designation.

Gemini 3.5 Flash features Thinking as a supported capability.

The input token parameter stands at 1,048,576 for both.

The output token parameter reaches 65,536 for Gemini 3.1 Pro.

It reaches 65,535 for Gemini 3.5 Flash.

Gemini 3.1 Pro includes explicit context caching and implicit context caching.

These elements guide the choice.

The framework directs alignment of requirements with these documented specifications.

This keeps the selection process grounded in original data from official documentation.

Frequently Asked Questions