GoogleGemini 3.1 ProVSGoogleGemini 3.5 Flash

Analysis by:the whichllmmodel Editorial Team|Updated: June 2026

Our Take

We recommend Gemini 3.5 Flash for a 1.3x API cost saving at identical performance levels. While both models deliver similar intelligence, Gemini 3.5 Flash is the optimal choice for high-volume pipelines. Choose Gemini 3.5 Flash for budget efficiency without sacrificing quality.

▶WHY?

Benchmark Calculations & Evidence:

Performance Match: Both models perform almost identically, with an average score gap of just 1.5% across reasoning and coding benchmarks.

Coding Benchmarks: Both models were evaluated on the SWE-bench Pro benchmark. Gemini 3.1 Pro scored 54.2%, while Gemini 3.5 Flash scored 55.1%.

Reasoning Benchmarks: Both models were evaluated on the GPQA Diamond benchmark. Gemini 3.1 Pro scored 94.3%, while Gemini 3.5 Flash scored 92.2%.

Cost Efficiency: Gemini 3.5 Flash pricing ($1.5/M input, $9/M output) is 1.3x cheaper than Gemini 3.1 Pro ($2/M input, $12/M output).

Was this recommendation helpful?

Model Specs

Gemini 3.1 Pro

Website

Benchmarks & Scores

Coding (swe-bench-pro)

54.2%

complex codebases, multi-file repositories, and architectural planning

Reasoning (gpqa-diamond)Winner (+2.1%)

94.3%

graduate-level science QA

Cost & Context

Cost (per 1M tokens)

$4.50Input: $2.00 | Output: $12.00

Context Window

1.05M tokens

Model Specs

Gemini 3.5 Flash

Website

Benchmarks & Scores

Coding (swe-bench-pro)Winner (+0.9%)

55.1%

complex codebases, multi-file repositories, and architectural planning

Reasoning (gpqa-diamond)

92.2%

graduate-level science QA

Cost & Context

Cost (per 1M tokens)1.3x cheaper

$3.38Input: $1.50 | Output: $9.00

Context Window

1.05M tokens

Read our data collection methodology

Frequently Asked Questions about Gemini 3.1 Pro vs Gemini 3.5 Flash

Gemini 3.5 Flash is cheaper than Gemini 3.1 Pro. Gemini 3.5 Flash has a blended cost of $3.38/1M tokens, which is about 1.3x cheaper than Gemini 3.1 Pro at $4.50/1M tokens.

Gemini 3.5 Flash is better for coding tasks on this benchmark. It scores 55.1% on swe-bench-pro (complex codebases, multi-file repositories, and architectural planning) compared to Gemini 3.1 Pro which scores 54.2%.

Related Matchups

Explore similar comparisons for Gemini 3.1 Pro and Gemini 3.5 Flash.

Browse More Comparisons

GoogleGemini 3.1 Pro

OpenAIGPT-5.5

Compare Specs

GoogleGemini 3.5 Flash

Do you want to find a model for your constraints?

Use our interactive model finder to filter LLMs by reasoning capability, coding performance, cost, and context length.

Open Model Finder