Gemini 1.5 Pro vs Gemini 2.5 Flash Preview (thinking)

Compare Gemini 1.5 Pro and Gemini 2.5 Flash Preview (thinking), both from Google AI, context windows of 1.0M vs 1.0M, tested across 11 shared challenges. Updated April 2026.

Which is better, Gemini 1.5 Pro or Gemini 2.5 Flash Preview (thinking)?

Gemini 1.5 Pro and Gemini 2.5 Flash Preview (thinking) are both competitive models. Gemini 1.5 Pro costs $3.5/M input tokens vs $0.175/M for Gemini 2.5 Flash Preview (thinking). Context windows: 1000K vs 1049K tokens. Compare their real outputs side by side below.

Key Differences Between Gemini 1.5 Pro and Gemini 2.5 Flash Preview (thinking)

Gemini 1.5 Pro is made by google while Gemini 2.5 Flash Preview (thinking) is from google. Gemini 1.5 Pro has a 1000K token context window compared to Gemini 2.5 Flash Preview (thinking)'s 1049K. On pricing, Gemini 1.5 Pro costs $3.5/M input tokens vs $0.175/M for Gemini 2.5 Flash Preview (thinking).

Our Verdict
Gemini 1.5 Pro
Gemini 1.5 Pro
Gemini 2.5 Flash Preview (thinking)
Gemini 2.5 Flash Preview (thinking)

No community votes yet. On paper, these are closely matched - try both with your actual task to see which fits your workflow.

Gemini 2.5 Flash Preview (thinking) is 3.0x cheaper per token — worth considering if cost matters.

Too close to call
Writing DNA

Style Comparison

Similarity
99%

Gemini 1.5 Pro uses 8.1x more headings

Gemini 1.5 Pro
Gemini 2.5 Flash Preview (thinking)
61%Vocabulary53%
15wSentence Length14w
0.80Hedging0.38
3.7Bold4.4
3.3Lists4.1
0.00Emoji0.00
0.08Headings0.00
0.09Transitions0.24
Based on 8 + 7 text responses
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Gemini 1.5 ProGemini 2.5 Flash Preview (thinking)

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