Gemini 1.5 Pro vs Gemini 3.1 Pro Preview

Compare Gemini 1.5 Pro and Gemini 3.1 Pro Preview, both from Google AI, context windows of 1.0M vs 1.0M, tested across 18 shared challenges. Updated April 2026.

Which is better, Gemini 1.5 Pro or Gemini 3.1 Pro Preview?

Gemini 1.5 Pro and Gemini 3.1 Pro Preview are both competitive models. Gemini 1.5 Pro costs $3.5/M input tokens vs $2/M for Gemini 3.1 Pro Preview. Context windows: 1000K vs 1049K tokens. Compare their real outputs side by side below.

Key Differences Between Gemini 1.5 Pro and Gemini 3.1 Pro Preview

Gemini 1.5 Pro is made by google while Gemini 3.1 Pro Preview is from google. Gemini 1.5 Pro has a 1000K token context window compared to Gemini 3.1 Pro Preview's 1049K. On pricing, Gemini 1.5 Pro costs $3.5/M input tokens vs $2/M for Gemini 3.1 Pro Preview.

Our Verdict
Gemini 3.1 Pro Preview
Gemini 3.1 Pro Preview
Gemini 1.5 Pro
Gemini 1.5 ProRunner-up

No community votes yet. On paper, Gemini 3.1 Pro Preview has the edge — bigger model tier, newer.

Too close to call
Writing DNA

Style Comparison

Similarity
97%

Gemini 3.1 Pro Preview uses 8.9x more headings

Gemini 1.5 Pro
Gemini 3.1 Pro Preview
61%Vocabulary54%
15wSentence Length18w
0.80Hedging0.29
3.7Bold4.9
3.3Lists3.3
0.00Emoji0.00
0.08Headings0.72
0.09Transitions0.14
Based on 8 + 23 text responses
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Ask them anything yourself

Gemini 1.5 ProGemini 3.1 Pro Preview

279 AI models invented the same fake scientist.

We read every word. 250 models. 2.14 million words. This is what we found.

AI Hallucination Index 2026
Free preview13 of 58 slides
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