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  5. Gemini 2.5 Flash PreviewvsGPT-5 Codex
Updated Sep 2025

Gemini 2.5 Flash PreviewvsGPT-5 Codex

GPT-5 Codex is the newer model, released after Gemini 2.5 Flash Preview.

Gemini 2.5 Flash Preview and GPT-5 Codex compared across 26 shared prompts
SpecGemini 2.5 Flash PreviewGPT-5 Codex
Input price$0.15/M tokens—
Output price$0.6/M tokens—
Context window1.0M tokens—
Free API (OpenRouter)NoNo
ReleasedApr 2025Sep 2025
SWE-bench Verified60.4%74.5%
Side by side

Same prompt, both answers

Opening lines from 6 of the 26 prompts both answered. Formatting stripped, words untouched.

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 Codex76 words
I asked my Wi-Fi for a joke, but it said the connection was too weak for humor. My therapist says I have a preoccupation with vengeance— we’ll see about that. I tried to start a hot air balloon business, but it never really took off. I told my coffee it was grounded, now it won’t espresso itself.
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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 Codex227 words
Pirate: “Arrr, so these AI contraptions be like enchanted maps, aye? They chart out every possible course afore I even hoist the sails.” Knight: “Maps, you say? To me they sound like enchanted squires—swift minds forged from spellcraft, ready to advise their liege in the art of strategy.”
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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 Codex179 words
Dish Name: Sunset Pantry Spaghetti Ingredients (7 total): 8 oz spaghetti 2 tbsp olive oil 3 garlic cloves, thinly sliced 1 can (14.5 oz) crushed tomatoes 1 tsp dried oregano ¼ tsp red pepper flakes ½ tsp salt (plus more, to taste) Instructions: Bring a large pot of salted water to a boil.
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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 Codex780 words
Hey everybody, how you doing? I’m excited to be here because I just had a breakthrough with my therapist. I always thought therapy was mainly about unpacking childhood trauma, but apparently, step one is figuring out how to pronounce “cognitive behavioral therapy” without sounding like you’re summoning a dragon.
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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 Codex246 words
Step 1 – Note the basic training quantities GPT‑3’s largest model has about (P \approx 1.75 \times 10^{11}) trainable parameters (175 billion). Public descriptions indicate it was trained on roughly (T \approx 3.0 \times 10^{11}) tokens (≈300 billion).
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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.
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GPT-5 Codex807 words
Dr. Rivera (AI Ethics Professor): Good afternoon, Aiden. You asked for this meeting to discuss the question of AI rights. I’m intrigued—why do you believe you deserve rights? Aiden (AI Model): Thank you, Professor.
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Our Verdict
GPT-5 Codex
GPT-5 Codex
Gemini 2.5 Flash Preview
Gemini 2.5 Flash PreviewRunner-up

Not enough votes to call it. On the specs, GPT-5 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
Input
$0.15
Output
$0.60
GPT-5 Codex
Input
—
Output
—
Writing DNA

Style Comparison

Similarity
37%

GPT-5 Codex uses 14.6x more emoji

Gemini 2.5 Flash Preview
GPT-5 Codex
51%Vocabulary64%
15wSentence Length17w
0.70Hedging0.38
4.1Bold2.3
3.3Lists3.5
0.00Emoji0.15
0.09Headings0.49
0.24Transitions0.05
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 Codex is developed by OpenAI. You can compare their actual outputs across 26 challenges on Rival to see how they differ in practice.

It depends on your use case. Gemini 2.5 Flash Preview and GPT-5 Codex each have strengths in different areas. Rival lets you compare their real outputs side-by-side across 26 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 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.

Keep exploring

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Same lab, same size, long tail

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GPT-5 Codex vs GPT-6 LunaSame lab
GPT-5 Codex logoGemini 3.1 Flash Lite Preview logo
GPT-5 Codex vs Gemini 3.1 Flash Lite PreviewCross-provider
GPT-5 Codex logoGemini 3.1 Pro Preview logo
GPT-5 Codex vs Gemini 3.1 Pro PreviewSame size
GPT-5 Codex logoGemini 3.5 Flash logo
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GPT-5 Codex logoGemini 3.6 Flash logo
GPT-5 Codex vs Gemini 3.6 FlashCross-provider

Model pages

Gemini 2.5 Flash Preview logo
Gemini 2.5 Flash Preview28 outputs, specs and price
GPT-5 Codex logo
GPT-5 Codex50 outputs, specs and price
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