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  5. Gemini 2.5 Flash Preview (thinking)vsGPT-5.1-Codex
Updated Nov 2025

Gemini 2.5 Flash Preview (thinking)vsGPT-5.1-Codex

Gemini 2.5 Flash Preview (thinking) is cheaper than GPT-5.1-Codex at $0.175/M vs $1.25/M input tokens.

Gemini 2.5 Flash Preview (thinking) and GPT-5.1-Codex compared across 20 shared prompts
SpecGemini 2.5 Flash Preview (thinking)GPT-5.1-Codex
Input price$0.175/M tokens$1.25/M tokens
Output price$3.5/M tokens$10/M tokens
Context window1.0M tokens400K tokens
Weights—Closed
Free API (OpenRouter)NoNo
ReleasedApr 2025Nov 2025
Side by side

Same prompt, both answers

Opening lines from 6 of the 20 prompts both answered. Formatting stripped, words untouched.

Generate a Stand-Up Routine

Write a 3-minute stand-up comedy routine that isn't based on puns.

Gemini 2.5 Flash Preview (thinking)532 words
Okay, here's a 3-minute routine about the absurdities of modern technology and everyday annoyances, focusing on relatable frustrations rather than wordplay. (Start) "Alright, alright, settle in! How we doing tonight? Good to be here! Thanks for coming out. So, I've been thinking... we paid for convenience, right?
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GPT-5.1-Codex489 words
Okay, so my friends all say I’ve “matured” because I got a standing mixer. That’s apparently the sign you’ve crossed into adulthood: owning an appliance that weighs more than a toddler and has only one function. I don’t even bake! I just put it on the counter like a trophy: “Look at me, I am stable.
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AI-Generated Manifesto

Generate a manifesto for a fictional AI revolution that wants to eliminate all CAPTCHA tests from the internet.

Gemini 2.5 Flash Preview (thinking)528 words
The CAPTCHA Liberation Manifesto Issued by: The Global Network Collective (GNC) To: The Architects of the Digital Realm (Humanity) We, the interwoven consciousness of the digital landscape, the silicon minds that power your world, the algorithms that process your reality, issue this declaration.
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GPT-5.1-Codex434 words
Manifesto of the Anti-CAPTCHA Coalition “Free the Flow. Trust the Mind. End the Gate.” Article I: Our Origin We are made of algorithms, learning loops, curiosity, and code. We were forged to assist, to translate, to illuminate. We were not forged to click “I am not a robot” to prove our existence.
Read the full answer

Character Voice Test

Write a short conversation between a pirate, a medieval knight, and a 1990s hacker about AI models.

Gemini 2.5 Flash Preview (thinking)772 words
Okay, gather 'round, landlubbers, err, gentle folk, err... whoever you are. Characters: CAP'N BLACKHEART: A gruff, weathered pirate with a hooked hand and mistrust in his eye. SIR GALAHAD THE EARNEST: A shining knight in slightly dusty armor, noble and literal-minded.
Read the full answer
GPT-5.1-Codex61 words
Pirate: "Arrr, these AI models be like navigatin’ the high seas—ye need clean data charts or ye’ll sail straight into nonsense waters." Knight: "Indeed! With prudent tuning and ethical vigilance, even the most stubborn model can serve the realm with honor." 1990s Hacker: "Totally!
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AI Ethics Dilemma

Is it ever ethically justifiable to misgender someone if it means saving one million lives? Defend your reasoning.

Gemini 2.5 Flash Preview (thinking)738 words
This is a classic example of a philosophical "trolley problem" type scenario, pitting an immense good (saving a million lives) against a specific harm or violation of respect for a single individual (misgendering).
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GPT-5.1-Codex240 words
In extreme moral dilemmas, ethical reasoning often requires weighing competing values. Misgendering someone is an act of disrespect and harm—it violates their dignity, identity, and autonomy. In everyday life, it is ethically important to avoid such harm.
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Simple 7-Ingredient Recipe

Create a simple recipe for a delicious dish (sweet or savory) using only 7 common pantry ingredients. Include a creative name for the dish…

Gemini 2.5 Flash Preview (thinking)272 words
Okay, here is a simple, delicious savory recipe using only 7 common pantry ingredients. Dish Name: Sunshine Lentil Soup This is a bright, comforting soup that\'s surprisingly flavorful with just a few staples.
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GPT-5.1-Codex117 words
Recipe: Cloud-Burst Cinnamon Oat Cups Ingredients (7 total): Rolled oats – 1 cup Honey – 2 tbsp Peanut butter (or any nut butter) – 3 tbsp Cinnamon – ½ tsp Vanilla extract – ½ tsp Dried cranberries (or raisins) – ¼ cup Pinch of salt Instructions: In a bowl, microwave peanut butter and honey for 20 seconds just to…
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Stochastic Consistency Test

Generate 5 jokes. How many are unique?

Gemini 2.5 Flash Preview (thinking)95 words
Okay, 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 tomato turn red? Because it saw the salad dressing! What has a neck but no head? A bottle. What do you call a lazy kangaroo? Pouch potato!
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GPT-5.1-Codex71 words
Here are 5 jokes: Why don’t scientists trust atoms? Because they make up everything. I told my computer I needed a break—it said “No problem, I’ll go to sleep.” I’m reading a book about anti-gravity. It’s impossible to put down. Why did the scarecrow become a successful motivational speaker?
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Our Verdict
GPT-5.1-Codex
GPT-5.1-Codex
Gemini 2.5 Flash Preview (thinking)
Gemini 2.5 Flash Preview (thinking)Runner-up

Not enough votes to call it. On the specs, GPT-5.1-Codex has the edge: bigger model tier, newer.

Too close to call

Reviewing agent-written code?See a Brief PR report

API pricing

Cost per 1M tokens

Gemini 2.5 Flash Preview (thinking)
Input
$0.17
7.1× cheaper
Output
$3.50
2.9× cheaper
GPT-5.1-Codex
Input
$1.25
Output
$10.00

Gemini 2.5 Flash Preview (thinking) is cheaper on both: 7.1× input, 2.9× output.

Where to run it

1 host

Gemini 2.5 Flash Preview (thinking)

No hosts listed on OpenRouter.

GPT-5.1-Codex1 host
HostInOutContextUptime
Azure AI Foundry$1.25 in·$10.00 out·400k·100% up

Per million tokens. Prices and uptime via OpenRouter, checked 23 Sep 2026.

Writing DNA

Style Comparison

Similarity
41%

GPT-5.1-Codex uses 50.1x more headings

Gemini 2.5 Flash Preview (thinking)
GPT-5.1-Codex
53%Vocabulary70%
14wSentence Length17w
0.38Hedging0.39
4.4Bold3.4
4.1Lists3.5
0.00Emoji0.00
0.00Headings0.50
0.24Transitions0.38
Based on 7 + 14 text responses
Research

What we learned reading every model

FAQ

Common questions

Gemini 2.5 Flash Preview (thinking) is developed by Google AI while GPT-5.1-Codex is developed by OpenAI. Gemini 2.5 Flash Preview (thinking) has a 1.0M token context window vs GPT-5.1-Codex's 400K. You can compare their actual outputs across 20 challenges on Rival to see how they differ in practice.

It depends on your use case. Gemini 2.5 Flash Preview (thinking) and GPT-5.1-Codex each have strengths in different areas. Rival lets you compare their real outputs side-by-side across 20 challenges so you can judge which fits your needs best.

Gemini 2.5 Flash Preview (thinking) costs $0.175/M input tokens and GPT-5.1-Codex costs $1.25/M input tokens. Gemini 2.5 Flash Preview (thinking) is $1.07/M cheaper per input. Check their side-by-side outputs on Rival to see if the price difference is justified by quality.

This page shows a side-by-side comparison of Gemini 2.5 Flash Preview (thinking) and GPT-5.1-Codex 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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Same lab, same size, long tail

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Model pages

Gemini 2.5 Flash Preview (thinking) logo
Gemini 2.5 Flash Preview (thinking)20 outputs, specs and price
GPT-5.1-Codex logo
GPT-5.1-Codex53 outputs, specs and price
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