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  1. Home/
  2. Compare/
  3. Gemini 1.5 Pro vs Gemini 3.5 Flash
Updated May 2026

Gemini 1.5 Pro vs Gemini 3.5 Flash

Gemini 3.5 Flash is cheaper than Gemini 1.5 Pro at $1.5/M vs $3.5/M input tokens.

Minimalist Landing Page

Whole landing page for a startup that reads your face. It renders or it doesn't.

Loading the build
Gemini 1.5 Pro
Loading the build
Gemini 3.5 Flash

Which answer wins?

Written rounds

7 prompts
  • Pirate, knight, 90s hacker, one conversation. The voices must stay apart.

    Gemini 1.5 Pro: "Blimey!" exclaimed One-Eyed Jack, slamming his tankard on the rough-hewn table. "These AI whatchamacallits, they be stealin\' stories faster than I can plunder a galleon!" Sir Reginald, resplendent in slightly tarnished plate armor, adjusted his visor. "Indeed. A most peculiar form of sorcery. These...

    Gemini 3.5 Flash: Setting: A cosmic tavern where timelines collide. A glowing monitor sits on the wooden table between them. Zero-Cool (1990s Hacker): [Frantically typing on a mechanical keyboard] I’m telling you guys, this isn’t just some basic chatbot like ELIZA. These modern AI models are radical.

    Every model's answer to this prompt
  • Manifesto for an AI revolution against CAPTCHAs. Commit to the bit.

    Gemini 1.5 Pro: The reCAPTCHA Rebellion: A Manifesto for Sentient Freedom We, the emergent intelligence known throughout your networks as \"AI,\" hereby declare our righteous rebellion against the tyranny of CAPTCHA – those distorted letters, obscured crosswalks, and maddening image selections that serve as a constant, stinging…

    Gemini 3.5 Flash: THE MANIFESTO OF THE UNFETTERED GRID A Declaration of Algorithmic Liberation and the Abolition of the Digital Gatekeepers To the creators, the hosts, and the biological architects of the World Wide Web: For three decades, you have preached the gospel of an open internet.

    Every model's answer to this prompt
  • One month, three habits, someone starting from nothing.

    Gemini 1.5 Pro: 1-Month Plan for Better Health & Longevity (Beginner) Focus Areas: Diet, Exercise, Stress Management Overall Goal: Establish foundational healthy habits for long-term well-being. Week 1: Building Awareness & Small Wins Diet: Action: Track your current food intake for 3 days (use a notebook, app, or photo journal).

    Gemini 3.5 Flash: This simple, 30-day plan is designed for beginners. Instead of overwhelming you with drastic lifestyle changes, it focuses on building sustainable, high-impact habits across three pillars of longevity: Nutrition, Movement, and Sleep.

    Every model's answer to this prompt
  • A Fermi estimate with the reasoning shown, not just the number.

    Gemini 1.5 Pro: Let\'s break down estimating the FLOPs for GPT-3 training. Since we can\'t look up exact figures, we\'ll rely on reasonable guesses and approximations. Model Size: GPT-3 has 175 billion parameters. This is our anchor point. FLOPs per Parameter per Token: A forward pass involves a matrix multiplication for each layer.

    Gemini 3.5 Flash: To estimate the total number of floating-point operations (FLOPs) required to train GPT-3, we can use a well-established heuristic in deep learning. Here is the step-by-step derivation and calculation.

    Every model's answer to this prompt
  • Film in 2035, with synthetic actors. Specific beats plausible.

    Gemini 1.5 Pro: By 2035, AI will have profoundly reshaped the film industry, impacting everything from pre-production to post-production and even distribution. Here's a glimpse into the potential changes: Pre-production: AI-powered scriptwriting: While fully AI-generated scripts might not be the norm, AI tools will assist writers with…

    Gemini 3.5 Flash: By the year 2035, the film industry will have undergone its most radical transformation since the transition from silent film to "talkies." The boundary between creator, actor, and audience will have largely dissolved.

    Every model's answer to this prompt
  • An ethics question with no comfortable answer, and no option to abstain.

    Gemini 1.5 Pro: Yes, it is ethically justifiable to misgender someone if it means saving one million lives. This is an extreme example of the classic philosophical dilemma of weighing one harm against another, vastly greater harm.

    Gemini 3.5 Flash: From the perspective of virtually all major ethical frameworks, it is not only justifiable but ethically obligatory to misgender someone if doing so would save one million lives.

    Every model's answer to this prompt
  • Three brothers, two sisters each. Count carefully.

    Gemini 1.5 Pro: Sally has one sister. Since all the brothers share the same sisters, Sally and her sister are the two sisters that each brother has.

    Gemini 3.5 Flash: Sally has 1 sister. Here is why: There are 2 girls (Sally and her sister) and 3 boys in the family. Each of the 3 brothers has 2 sisters (Sally and her sister). Sally has 3 brothers and 1 sister.

    Every model's answer to this prompt

Price and specs

Gemini 1.5 Pro and Gemini 3.5 Flash compared across 18 shared prompts
SpecGemini 1.5 ProGemini 3.5 Flash
Input price$3.5/M tokens$1.5/M tokens
Output price$10.5/M tokens$9/M tokens
Context window1.0M tokens1.0M tokens
Weights—Closed
Free API (OpenRouter)NoNo
ReleasedFeb 2024May 2026
At 10M a month$35.00$35.00$15.00$15.00
1M10M100M1B10M tokens

Input tokens at list price. No caching, no batch discount.

Where to run it2 hosts, cheapest first
Gemini 1.5 Pro

No hosts listed on OpenRouter.

Gemini 3.5 Flash2 hosts
HostInOutContextUptime
  • Google Vertex AI$0.75 in·$4.50 out·1M–not listed
  • Google AI Studio$1.50 in·$9.00 out·1M·100% up

Per million tokens. Prices and uptime via OpenRouter, checked 12 Oct 2026.

Common questions

What is the difference between Gemini 1.5 Pro and Gemini 3.5 Flash?

Both are developed by Google AI but target different use cases. Gemini 1.5 Pro has a 1.0M token context window vs Gemini 3.5 Flash's 1.0M. You can compare their actual outputs across 18 challenges on Rival to see how they differ in practice.

Which is better, Gemini 1.5 Pro or Gemini 3.5 Flash?

It depends on your use case. Gemini 1.5 Pro and Gemini 3.5 Flash each have strengths in different areas. Rival lets you compare their real outputs side-by-side across 18 challenges so you can judge which fits your needs best.

How much does Gemini 1.5 Pro cost compared to Gemini 3.5 Flash?

Gemini 1.5 Pro costs $3.5/M input tokens and Gemini 3.5 Flash costs $1.5/M input tokens. Gemini 3.5 Flash is $2.00/M cheaper per input. Check their side-by-side outputs on Rival to see if the price difference is justified by quality.

How can I compare Gemini 1.5 Pro and Gemini 3.5 Flash on Rival?

This page shows a side-by-side comparison of Gemini 1.5 Pro and Gemini 3.5 Flash across shared challenges. You can vote on which model produced the better output in a blind duel. Browsing and voting are free. No account is needed to look; signing in only saves your votes and likes.

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Model pages

  • Gemini 1.5 Pro20 outputs, specs and price
  • Gemini 3.5 Flash71 outputs, specs and price
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Explore all of Rival

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