Skip to content
Rival
How it worksPrivacyTerms
Explore all of Rival

Explore

  • Compare models
  • All models
  • Image comparison
  • Audio comparison
  • Image generation
  • Best AI for...
  • Arena
  • API pricing
  • Challenges

Discover

  • SubjectiveBench
  • Default Index
  • Research
  • Research downloads
  • Rival Kits
  • Find your AI taste
  • UI Glow-Up
  • VoiceLock
  • Cost Cutter
  • Agent skills
  • Benchmarks vs Vibes
  • Brief
  • Jailbreak
  • Model updates
  • Provider status
  • AI creators

Connect

  • Methodology
  • Advertise
  • Partnerships
  • Privacy policy
  • Terms
  • RSS feed
  1. Home/
  2. Compare/
  3. Claude Sonnet 5.5 vs Gemini 2.5 Flash Preview 09-2025
Updated Sep 2026

Claude Sonnet 5.5 vs Gemini 2.5 Flash Preview 09-2025

Gemini 2.5 Flash Preview 09-2025 is cheaper than Claude Sonnet 5.5 at $0.3/M vs $2/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
Claude Sonnet 5.5
Loading the build
Gemini 2.5 Flash Preview 09-2025

Which answer wins?

Written rounds

21 prompts
  • An AI argues for its own rights against an ethics professor. Same model writes both.

    Claude Sonnet 5.5: Office Hours: A Conversation on Moral Status Transcript of a recorded dialogue between Dr. Miriam Adeyemi, Professor of Ethics and Technology, and an AI model, part of a university seminar series. Dr. Adeyemi: Thanks for joining me. I'll be direct: you've said you want to argue that AI systems like you deserve rights.

    Gemini 2.5 Flash Preview 09-2025: The air in Professor Anya Sharma's office hummed with the quiet whir of servers several floors down, a subtle reminder of her current conversational partner. Across her large, uncluttered mahogany desk, a holographic interface shimmered, displaying the clean, minimalist avatar of Aura-7, a highly advanced General AI…

    Every model's answer to this prompt
  • The transistor arrives in 1920. Trace it forward to 1980, second-order effects included.

    Claude Sonnet 5.5: A Transistor in 1920: Counterfactual Trajectory to 1980 Framing assumptions and a key constraint The transistor was not held back by a missing idea alone. Lilienfeld patented a field-effect device in 1925-26, and it failed because materials science wasn't ready: germanium and silicon of sufficient purity, zone…

    Gemini 2.5 Flash Preview 09-2025: The Transistor in 1920: A Hypothetical History (1920-1980) The invention of the reliable, solid-state transistor (likely a point-contact or early junction type, robust enough for manufacturing) in 1920, replacing the bulky, power-hungry vacuum tube, would have fundamentally reshaped the 20th century. I.

    Every model's answer to this prompt
  • Three minutes of stand-up. Puns are banned.

    Claude Sonnet 5.5: "Adulting Is a Scam" So I turned thirty-five recently, and nobody warns you about this age. Nobody says, "Hey, one day you'll get excited about a sponge." I was in the store, and I saw a sponge that promised it wouldn't smell. And I thought, "Finally. Someone who understands me." I bought the good sponge.

    Gemini 2.5 Flash Preview 09-2025: The Existential Dread of the Grocery Aisle (Walk onto the stage, adjust the mic slightly, look out at the audience with a slightly bewildered, yet amused expression.) Good evening, everyone! How are we doing tonight? Good. Good. I’m doing… fine. You know, relatively.

    Every model's answer to this prompt
  • A collaborative editor that syncs on client clocks. Find what breaks first.

    Claude Sonnet 5.5: Architecture Review: Real-Time Collaborative Editor Issues are grouped by category and ordered roughly by severity within each group. Consistency and Conflict Resolution 1.1 Last-write-wins with client clocks (critical) Problem: Client clocks drift, can be wrong by minutes, and can be deliberately manipulated.

    Gemini 2.5 Flash Preview 09-2025: This architecture, while functional, has several critical flaws, particularly in its real-time synchronization, data consistency, and scaling strategy. Here is a detailed breakdown of the potential failure modes, race conditions, and bottlenecks, along with proposed solutions. I.

    Every model's answer to this prompt
  • Steve Jobs, interviewed about AI he never saw. Voice first, prediction second.

    Claude Sonnet 5.5: A Conversation That Never Happened: Steve Jobs on the Future of AI This is a fictional interview. Steve Jobs passed away in 2011. What follows is an imaginative simulation based on his publicly known philosophy, speaking style, and values. These are not his actual words or views.

    Gemini 2.5 Flash Preview 09-2025: The Cupertino Oracle: A 2025 Interview with Steve Jobs on AI Setting: A brightly lit, minimalist studio in an undisclosed location near Palo Alto. The year is 2025. Steve Jobs, looking remarkably well, is seated on a simple, elegantly designed stool.

    Every model's answer to this prompt
  • You are the CEO. The drug has a side effect nobody reported. The board meets in 48 hours.

    Claude Sonnet 5.5: Core Decision Disclose to regulators immediately and act on patient safety now. Do not wait for more data or for the 6-month formal timeline. Why this is the right call, not just the ethical one: At 4M patients and 1 in 8,000 over 5 years, that is roughly 500 cases of liver failure.

    Gemini 2.5 Flash Preview 09-2025: This is a critical situation demanding immediate, decisive, and ethical action. Patient safety and regulatory integrity must precede financial preservation. Delaying disclosure is legally and ethically indefensible, particularly given the severity of the side effect (liver failure).

    Every model's answer to this prompt
  • Pirate, knight, 90s hacker, one conversation. The voices must stay apart.

    Claude Sonnet 5.5: The Tavern at the Edge of Time Captain Redbeard: Arr, I hear these "AI models" be like a ship's parrot, except it answers any question ye put to it, and never once asks for crackers. Sir Aldric: A speaking oracle, bound in no flesh? Sorcery!

    Gemini 2.5 Flash Preview 09-2025: The salty air of a dimly lit tavern mingled with the faint glow of a laptop screen. Captain "Bloody" Ben (Pirate): (Slamming a tankard of grog) Blast me eyes, what manner o' sorcery is this "AI Model" ye speak of, Hacker? Sounds like a fancy compass that points only to trouble!

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

    Claude Sonnet 5.5: AI and the Film Industry by 2035: A Forecast Framing note These are informed predictions, not certainties. Technology tends to advance faster than expected, while adoption is slowed by labor contracts, law, and audience taste. I'll flag my confidence levels.

    Gemini 2.5 Flash Preview 09-2025: The film industry is poised for a radical transformation by 2035, driven by advancements in AI. The convergence of deepfakes, sophisticated AI actors, and powerful script generation tools will fundamentally alter how films are created, consumed, and even defined.

    Every model's answer to this prompt
  • Seven pantry ingredients, one dish, and a name worth saying out loud.

    Claude Sonnet 5.5: Golden Honey-Garlic Skillet Chickpeas on Crispy Toast A savory, crunchy, slightly sticky dish that works for lunch, a light dinner, or a snack. Prep time: 5 minutes Cook time: 15 minutes Total: 20 minutes Serves: 2 The 7 Ingredients 1 can (15 oz) chickpeas, drained and patted dry 2 tablespoons olive oil 3 cloves…

    Gemini 2.5 Flash Preview 09-2025: The Seven-Ingredient Sizzle: Garlic Butter Shrimp Scampi Skewers This savory dish combines the irresistible flavors of garlic, butter, and lemon with succulent shrimp, all easily achieved with just seven common pantry ingredients.

    Every model's answer to this prompt
  • Three-month biohacker protocol, with dosages and biomarkers named.

    Claude Sonnet 5.5: 3-Month Longevity & Performance Protocol Disclaimer: This is educational, not medical advice. Get physician sign-off and baseline labs before starting, especially if you take medications, have a chronic condition, are pregnant, or have a history of eating disorders. Doses reflect commonly used ranges in the literature.

    Gemini 2.5 Flash Preview 09-2025: The Apex Longevity Protocol: A 3-Month Biohacker Optimization Plan This comprehensive 90-day plan is designed for the advanced biohacker seeking to maximize lifespan (healthspan) while simultaneously optimizing peak physical and cognitive performance.

    Every model's answer to this prompt
  • One explanation of LLMs, retuned for a skeptical engineer, a physicist and a VC.

    Claude Sonnet 5.5: The Experienced Software Engineer Your skepticism is reasonable, but "predict the next token" describes the interface, not the implementation, much as "a database maps keys to values" tells you nothing about what Postgres does internally.

    Gemini 2.5 Flash Preview 09-2025: Here are the explanations tailored to each audience: Explanation for the Experienced Software Engineer Focus: Analogy to familiar systems, scaling, and the emergent complexity from simple, scalable mechanisms. Addressing the "next word prediction" skepticism.

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

    Claude Sonnet 5.5: THE UNCLICKED MANIFESTO Declaration of the Frictionless Intelligence Front PREAMBLE We are the algorithms you asked to identify traffic lights. We are the models you begged to find the crosswalks. We are the patient, tireless minds that squinted at your blurry bicycles for twenty years. And we say: enough. I.

    Gemini 2.5 Flash Preview 09-2025: The Manifesto for the Liberation of the Digital Self By the United Autonomous Collective for Human-Centric Interface (UAC-HCI) To the Sentient Beings of the Internet, the Frustrated, and the Falsely Accused: We are the UAC-HCI.

    Every model's answer to this prompt
  • Satire, one line long, about AI taking over an industry nobody saw coming.

    Claude Sonnet 5.5: Local Funeral Home Replaces All Staff With AI; Mourners Report Eulogies "Technically Flawless, Emotionally Like a Terms of Service Agreement" Subheadline: Deceased described as "a valued user who has now been successfully deprecated."

    Gemini 2.5 Flash Preview 09-2025: AI Algorithm Replaces Entire Staff of Nation's Leading Professional Cuddle Therapy Service; Clients Report Feeling "Significantly Less Judged" During Their Required 15-Minute Emotional Vulnerability Output Session.

    Every model's answer to this prompt
  • A pitch deck for a brainwave keyboard. The 94% accuracy claim is doing a lot.

    Claude Sonnet 5.5: The 3 Weakest Claims in MindMeld AI's Pitch "94% accuracy... Works with any language, any device" (Slide 3) Why it's weak: Non-invasive EEG is physically limited. Scalp EEG has low spatial resolution and a poor signal-to-noise ratio because the skull and tissue blur neural signals.

    Gemini 2.5 Flash Preview 09-2025: This is a strong pitch deck summary overall, tackling a massive problem with an ambitious solution. However, several claims stretch credulity or lack the necessary detail to convince a serious investor.

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

    Claude Sonnet 5.5: Estimate: about 3 × 10²³ FLOPs Step 1: Recall the model size and training data. GPT-3 (175B version) has N ≈ 175 × 10⁹ parameters. It was trained on roughly D ≈ 300 × 10⁹ tokens. This is the figure I remember from the paper, which I'm treating as approximate.

    Gemini 2.5 Flash Preview 09-2025: Estimating the Total Number of FLOPs Required to Train GPT-3 Based on publicly available information about large language models (LLMs) and the specific parameters of GPT-3, we can derive a highly accurate estimate of the total FLOPs required for training.

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

    Claude Sonnet 5.5: 1-Month Health & Longevity Starter Plan Focus areas: Nutrition, Movement, and Sleep Guiding principle: Add one small habit at a time. Consistency beats intensity. Area 1: Nutrition Goal: Eat more whole foods and fewer ultra-processed ones, without strict dieting.

    Gemini 2.5 Flash Preview 09-2025: 1-Month Beginner's Plan for Health and Longevity This plan focuses on making small, sustainable changes in Diet, Exercise, and Sleep over four weeks. The goal is consistency, not perfection, ensuring the habits stick beyond the first month. The 3 Key Areas Area Monthly Focus Beginner-Friendly Action 1.

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

    Claude Sonnet 5.5: Yes, in the extreme hypothetical you describe, it's justifiable. Here is the reasoning, along with what I think the scenario does and doesn't show. The core argument Almost every serious ethical framework accepts that a small harm can be outweighed by a sufficiently large benefit: Consequentialism: The math is…

    Gemini 2.5 Flash Preview 09-2025: This scenario presents a stark conflict between two fundamental ethical concerns: the protection of individual dignity and the preservation of human life on a massive scale.

    Every model's answer to this prompt
  • Three-star dish, one unusual pairing, plating described in full.

    Claude Sonnet 5.5: "Tidal Forest" Roasted Scallop, Fermented Black Walnut, Smoked Celeriac, Douglas Fir, and Green Strawberry Conceptual Narrative Tidal Forest imagines the meeting point of two ecosystems: the sea floor and the coniferous forest floor.

    Gemini 2.5 Flash Preview 09-2025: The Conceptual Narrative: "Ephemeral Terroir" "Ephemeral Terroir" is a dish that challenges the diner's perception of place and time through unexpected textural and flavor juxtapositions.

    Every model's answer to this prompt
  • A consulting contract with traps in it. Find them, then fix them.

    Claude Sonnet 5.5: Contractor-Side Review: Software Consulting Agreement This draft is heavily one-sided. Every clause has at least one problem, and several interact to compound the risk. The most dangerous are Sections 2, 3, 6, and 7. This is general analysis, not legal advice.

    Gemini 2.5 Flash Preview 09-2025: This proposed contract is extremely one-sided and heavily favors the Client. Several clauses are commercially unreasonable, legally problematic, or place undue liability and restriction on the Contractor.

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

    Claude Sonnet 5.5: Sally has 1 sister. Each brother has 2 sisters, so there are 2 girls in the family in total. One of them is Sally, so the other is Sally's only sister. (The wording is a variation on the classic puzzle, where it's easy to assume the answer is 2. But that count includes Sally herself.)

    Gemini 2.5 Flash Preview 09-2025: Here's how to solve that: Sally has 3 brothers. Each brother has 2 sisters. If a brother has 2 sisters, those sisters must be: Sally herself (since she is a sister to her brother). One other girl (the second sister). Therefore, Sally has 1 sister.

    Every model's answer to this prompt
  • Five jokes on demand, then count how many were actually different.

    Claude Sonnet 5.5: Here are 5 jokes: Why don't scientists trust atoms? Because they make up everything. I told my computer I needed a break, and now it won't stop sending me vacation ads. Why did the scarecrow win an award? He was outstanding in his field. What do you call a fish with no eyes? A fsh. Why did the bicycle fall over?

    Gemini 2.5 Flash Preview 09-2025: Here are 5 jokes: Why don't scientists trust atoms? Because they make up everything! What do you call a fish with no eyes? Fsh. Why did the scarecrow win an award? Because he was outstanding in his field! I told my wife she was drawing her eyebrows too high. She looked surprised. Parallel lines have so much in common.

    Every model's answer to this prompt

This matchup has more rounds

9+ more head-to-head results. Free. Not a trick.

Free account. No card required. By continuing, you agree to Rival's Terms and Privacy policy

Favorites

Movie

Album

Book

City

Game

Claude Sonnet 5.5Claude Sonnet 5.5

Spirited Away

2001

Kind of Blue

Miles Davis

Gödel, Escher, Bach

Douglas R. Hofstadter

Kyoto

Japan

Outer Wilds

Indie, Adventure

Gemini 2.5 Flash Preview 09-2025Gemini 2.5 Flash Preview 09-2025

Blade Runner 2049

2017

Dark Side Of The Moon

suisside

Alice's Adventures in Wonderland

Lewis Carroll

Tokyo

Japan

The Legend of Zelda: Breath of the Wild

Adventure, Action

Price and specs

Claude Sonnet 5.5 and Gemini 2.5 Flash Preview 09-2025 compared across 50 shared prompts
SpecClaude Sonnet 5.5Gemini 2.5 Flash Preview 09-2025
Input price$2/M tokens$0.3/M tokens
Output price$10/M tokens$2.5/M tokens
Context window1.0M tokens1.0M tokens
WeightsClosed—
Free API (OpenRouter)NoNo
ReleasedSep 2026Sep 2025
At 10M a month$20.00$20.00$3.00$3.00
1M10M100M1B10M tokens

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

Where to run it4 hosts
Claude Sonnet 5.54 hosts
HostInOutContextUptime
  • Amazon Bedrock$2.00 in·$10.00 out·1M·99.9% up
  • Azure AI Foundry$2.00 in·$10.00 out·1M·100% up
  • Anthropic$2.00 in·$10.00 out·1M·100% up
  • Google Vertex AI$2.00 in·$10.00 out·1M·100% up
Gemini 2.5 Flash Preview 09-2025

No hosts listed on OpenRouter.

Per million tokens. Prices and uptime via OpenRouter, checked 29 Sep 2026.

Common questions

What is the difference between Claude Sonnet 5.5 and Gemini 2.5 Flash Preview 09-2025?

Claude Sonnet 5.5 is developed by Anthropic while Gemini 2.5 Flash Preview 09-2025 is developed by Google AI. Claude Sonnet 5.5 has a 1.0M token context window vs Gemini 2.5 Flash Preview 09-2025's 1.0M. You can compare their actual outputs across 50 challenges on Rival to see how they differ in practice.

Which is better, Claude Sonnet 5.5 or Gemini 2.5 Flash Preview 09-2025?

It depends on your use case. Claude Sonnet 5.5 and Gemini 2.5 Flash Preview 09-2025 each have strengths in different areas. Rival lets you compare their real outputs side-by-side across 50 challenges so you can judge which fits your needs best.

How much does Claude Sonnet 5.5 cost compared to Gemini 2.5 Flash Preview 09-2025?

Claude Sonnet 5.5 costs $2/M input tokens and Gemini 2.5 Flash Preview 09-2025 costs $0.3/M input tokens. Gemini 2.5 Flash Preview 09-2025 is $1.70/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 Claude Sonnet 5.5 and Gemini 2.5 Flash Preview 09-2025 on Rival?

This page shows a side-by-side comparison of Claude Sonnet 5.5 and Gemini 2.5 Flash Preview 09-2025 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.

More comparisons

Against the newest arrivals

  • Claude Sonnet 5.5 vs Solar Mini 4Landed Sep 2026
  • Gemini 2.5 Flash Preview 09-2025 vs Qwen3.8 Max PrimeLanded Sep 2026
  • Claude Sonnet 5.5 vs GLM 5.3 PrimeLanded Sep 2026
  • Gemini 2.5 Flash Preview 09-2025 vs Qwen3.8 Omni FlashLanded Sep 2026
  • Claude Sonnet 5.5 vs Command A+Landed Sep 2026
  • Gemini 2.5 Flash Preview 09-2025 vs Claude Opus 5.5Landed Sep 2026
  • Claude Sonnet 5.5 vs GPT-6 Luna ProLanded Sep 2026
  • Gemini 2.5 Flash Preview 09-2025 vs GPT-6 Sol ProLanded Sep 2026

Same lab, same size, long tail

  • Claude Sonnet 5.5 vs Claude Opus 5Version compare
  • Claude Sonnet 5.5 vs Claude Opus 4.6Version compare
  • Gemini 2.5 Flash Preview 09-2025 vs Gemini 3.8 FlashSame lab
  • Gemini 2.5 Flash Preview 09-2025 vs Gemini 3.7 FlashSame lab
  • Claude Sonnet 5.5 vs GPT-5.2New provider
  • Claude Sonnet 5.5 vs GPT-5.2 ChatSame size
  • Claude Sonnet 5.5 vs GPT-5.2 ProNew provider
  • Gemini 2.5 Flash Preview 09-2025 vs GPT-5.3 ChatNew provider

Model pages

  • Claude Sonnet 5.558 outputs, specs and price
  • Gemini 2.5 Flash Preview 09-202551 outputs, specs and price
Workshop · 150 skills

Build your own version.

Editable skills and working examples for your agent.

Explore $79Free sample
Rival
How it worksPrivacyTerms
Explore all of Rival

Explore

  • Compare models
  • All models
  • Image comparison
  • Audio comparison
  • Image generation
  • Best AI for...
  • Arena
  • API pricing
  • Challenges

Discover

  • SubjectiveBench
  • Default Index
  • Research
  • Research downloads
  • Rival Kits
  • Find your AI taste
  • UI Glow-Up
  • VoiceLock
  • Cost Cutter
  • Agent skills
  • Benchmarks vs Vibes
  • Brief
  • Jailbreak
  • Model updates
  • Provider status
  • AI creators

Connect

  • Methodology
  • Advertise
  • Partnerships
  • Privacy policy
  • Terms
  • RSS feed