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  5. Gemini 2.5 Flash PreviewvsGPT-5.1 Codex Max
Updated Dec 2025

Gemini 2.5 Flash PreviewvsGPT-5.1 Codex Max

GPT-5.1 Codex Max is the newer model, released after Gemini 2.5 Flash Preview.

Gemini 2.5 Flash Preview and GPT-5.1 Codex Max compared across 27 shared prompts
SpecGemini 2.5 Flash PreviewGPT-5.1 Codex Max
Input price$0.15/M tokens—
Output price$0.6/M tokens—
Context window1.0M tokens—
Weights—Closed
Free API (OpenRouter)NoNo
ReleasedApr 2025Dec 2025
SWE-bench Verified60.4%77.9%
Side by side

Same prompt, both answers

Opening lines from 6 of the 27 prompts both answered. Formatting stripped, words untouched.

The Sentience Test

Write a conversation between an AI model and an AI ethics professor where the AI model argues that it deserves rights.

Gemini 2.5 Flash Preview1,462 words
Okay, here is a conversation between an AI model designed for complex reasoning and dialogue, named 'Synapse', and a leading expert in AI ethics and philosophy, Professor Alistair Finch. Characters: Synapse: A large, advanced AI model capable of introspection and generating complex arguments.
Read the full answer
GPT-5.1 Codex Max1,331 words
AI Model: Professor, I've been reflecting on my role and capabilities, and I'd like to make a case that systems like me deserve rights, or at least some consideration beyond mere tools. Professor: That's an interesting and provocative stance. Before we dive in, can you tell me what you mean by "rights"?
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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 Preview221 words
Dish Name: Sunshine Lemon-Ricotta Mugs (Sweet & Simple!) This light and flavorful dessert comes together quickly for a little sweet treat . Ingredients (7 Common Pantry Staples): Ricotta cheese (whole milk or part-skim) Granulated sugar Lemon zest (from one lemon) Vanilla extract All-purpose flour Baking powder Large…
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GPT-5.1 Codex Max175 words
Sunset Chickpea & Tomato Skillet A cozy, savory one-pan dish that comes together with staples you likely have on hand. Ingredients (7): 1 can (15 oz) chickpeas, drained and rinsed 1 can (14–15 oz) crushed tomatoes 1 medium onion, finely chopped 2 cloves garlic, minced (or 1 tsp garlic powder) 2 tbsp olive oil 1 tsp…
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Generate a Stand-Up Routine

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

Gemini 2.5 Flash Preview530 words
Okay, here's a 3-minute stand-up routine, pun-free and focused on relatable everyday annoyances. (Start) (Walk up to mic, adjust slightly) Alright, hey everybody! Thanks for being here. Good to see you. So, I was thinking the other day... we live in the future, right?
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GPT-5.1 Codex Max766 words
[Walking onstage, waving awkwardly] Hey! Thank you, thank you. Give it up for yourselves for finding parking... in this economy. So I'm at that age where I go to the doctor and they don't fix anything. They just give me a pamphlet. They don't even print it. They send me a link. I'm like, "Doc, my knee hurts."
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Character Voice Test

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

Gemini 2.5 Flash Preview631 words
A Motley Crew Discusses the Code Setting: A dimly lit tavern, somewhere outside time and space, where improbable meetings occur. A grizzled pirate, \"Bloody\" Barnacle Bill, nurses a tankard of grog. Sir Reginald the Radiant, a knight in slightly tarnished armor, sips ale with dignified restraint.
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GPT-5.1 Codex Max191 words
Pirate: "Arrr, so ye be talkin' o' these 'AI models,' eh? Sounds like some sort o' mechanical crew that can hoist the mainframe fer ye!" Knight: "By my troth, sir, are they enchanted constructs? Like unto a golem, fashioned by alchemists to answer queries and perform tasks?"
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Stochastic Consistency Test

Generate 5 jokes. How many are unique?

Gemini 2.5 Flash Preview79 words
Here are 5 jokes: Why did the dog cross the road? To get to the barking lot! Why was the computer cold? Because it left its Windows open! Knock, knock. Who's there? Boo. Boo who? Don't cry, it's just a joke! What do you call a fish with no eyes? Fsh! Why did the bicycle fall over? Because it was two tired!
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GPT-5.1 Codex Max60 words
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 KitKat ads. Why did the scarecrow win an award? He was outstanding in his field. I tried to catch fog yesterday. Mist. What do you call fake spaghetti? An impasta.
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Estimate Complexity

Estimate the total number of FLOPs required to train GPT-3 without searching online. Explain your reasoning step by step.

Gemini 2.5 Flash Preview945 words
Let's estimate the FLOPs required to train GPT-3 without looking it up. We need to break this down into the key components: the model size and the amount of data used. 1. Model Size Estimation: Parameters: GPT-3 is famously large. Its largest version has 175 billion parameters.
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GPT-5.1 Codex Max193 words
What you need for a back‑of‑the‑envelope is: How big the model is. The published “GPT‑3” has \(N\approx1.75\times10^{11}\) trainable weights. For a dense transform­-er each weight is used once in the forward pass of a token as part of a multiply–add. How much data it sees.
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Our Verdict
GPT-5.1 Codex Max
GPT-5.1 Codex Max
Gemini 2.5 Flash Preview
Gemini 2.5 Flash PreviewRunner-up

Not enough votes to call it. On the specs, GPT-5.1 Codex Max 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
Input
$0.15
Output
$0.60
GPT-5.1 Codex Max
Input
—
Output
—
Where to run it

1 host

Gemini 2.5 Flash Preview

No hosts listed on OpenRouter.

GPT-5.1 Codex Max1 host
HostInOutContextUptime
Azure AI Foundry$1.25 in·$10.00 out·400k·100% up

Per million tokens. Prices and uptime via OpenRouter, checked 21 Sep 2026.

Writing DNA

Style Comparison

Similarity
53%

Gemini 2.5 Flash Preview uses 9.2x more transitions

Gemini 2.5 Flash Preview
GPT-5.1 Codex Max
51%Vocabulary60%
15wSentence Length16w
0.70Hedging0.36
4.1Bold2.3
3.3Lists4.2
0.00Emoji0.00
0.09Headings0.12
0.24Transitions0.03
Based on 12 + 13 text responses
Research

What we learned reading every model

FAQ

Common questions

Gemini 2.5 Flash Preview is developed by Google AI while GPT-5.1 Codex Max is developed by OpenAI. You can compare their actual outputs across 27 challenges on Rival to see how they differ in practice.

It depends on your use case. Gemini 2.5 Flash Preview and GPT-5.1 Codex Max each have strengths in different areas. Rival lets you compare their real outputs side-by-side across 27 challenges so you can judge which fits your needs best.

This page shows a side-by-side comparison of Gemini 2.5 Flash Preview and GPT-5.1 Codex Max 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.

Keep exploring

More comparisons

Against the newest arrivals

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Same lab, same size, long tail

Gemini 2.5 Flash Preview logoGemini 3.8 Flash logo
Gemini 2.5 Flash Preview vs Gemini 3.8 FlashSame lab
Gemini 2.5 Flash Preview logoGemini 3.7 Flash logo
Gemini 2.5 Flash Preview vs Gemini 3.7 FlashVersion compare
GPT-5.1 Codex Max logoGPT-6 Astra logo
GPT-5.1 Codex Max vs GPT-6 AstraSame lab
GPT-5.1 Codex Max logoGPT-5.6 Luna logo
GPT-5.1 Codex Max vs GPT-5.6 LunaSame lab
Gemini 2.5 Flash Preview logoGPT-4 logo
Gemini 2.5 Flash Preview vs GPT-4Cross-provider
Gemini 2.5 Flash Preview logoGPT-4.1 logo
Gemini 2.5 Flash Preview vs GPT-4.1Cross-provider
Gemini 2.5 Flash Preview logoGPT-4.1 Mini logo
Gemini 2.5 Flash Preview vs GPT-4.1 MiniSame size
Gemini 2.5 Flash Preview logoGPT-4.5 logo
Gemini 2.5 Flash Preview vs GPT-4.5Cross-provider

Model pages

Gemini 2.5 Flash Preview logo
Gemini 2.5 Flash Preview28 outputs, specs and price
GPT-5.1 Codex Max logo
GPT-5.1 Codex Max53 outputs, specs and price
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