Updated Nov 13, 2025

Our Verdict

GPT-5.1-Codex

Gemini 2.5 Pro (I/O Edition)

No community votes yet. On paper, these are closely matched - try both with your actual task to see which fits your workflow.

Too close to call

Writing DNA

Style Comparison

Similarity

100%

GPT-5.1-Codex uses 32.3x more transitions

GPT-5.1-Codex

Gemini 2.5 Pro (I/O Edition)

70%Vocabulary58%

17wSentence Length16w

0.39Hedging0.38

3.4Bold5.8

3.5Lists5.0

0.00Emoji0.00

0.50Headings0.63

0.38Transitions0.01

Based on 14 + 16 text responses

vs

Ask them anything yourself

GPT-5.1-Codex

Gemini 2.5 Pro (I/O Edition)

279 AI models invented the same fake scientist.

We read every word. 250 models. 2.14 million words. This is what we found.

AI Hallucination Index 2026

Free preview13 of 58 slides

Download the free preview or get all 58 slides for $49

FAQ

Common questions

Keep going

GPT-5.1-Codex vs Grok 3New provider

GPT-5.1-Codex vs Llama 4 MaverickNew provider

GPT-5.1-Codex vs Claude Opus 4New provider

GPT-5.1-CodexvsGemini 2.5 Pro (I/O Edition)

35 fights queued

Why GPT-5.1-Codex?

6 months newerNov 2025

Why Gemini 2.5 Pro (I/O Edition)?

Dead even. This one's a coin flip.

GPT-5.1-CodexGemini 2.5 Pro (I/O Edition)

Input price

$1.25/M

$1.25/M

Output price

$10.00/M

$10.00/M

Context

400K

—

Released

Nov 2025

May 2025

Favorites

GPT-5.1-CodexGemini 2.5 Pro (I/O Edition)

Movie

The Shawshank Redemption

The Shawshank Redemption

2001

2001

Album

Kind of Blue

The Dark

Book

Le città invisibili

Le città invisibili

The Hitch Hiker's Guide to the Galaxy

The Hitch Hiker's Guide to the Galaxy

City

Kyoto

Kyoto

Game

Portal 2

Portal 2

Shooter, Puzzle4.6

CHRONO

CHRONO

12 / 35

01

Estimate Complexityreasoning

Tests an AI's ability to make educated estimates based on technical knowledge

GPT-5.1-Codex

GPT-5.1-Codex

Openai · Nov 2025text

Nothing here. The model returned empty. We stared at it for a while.

Try this prompt

Gemini 2.5 Pro (I/O Edition)

Gemini 2.5 Pro (I/O Edition)

Google · May 2025text

Nothing here. The model returned empty. We stared at it for a while.

Try this prompt

Vote

2 / 35

02

Logic Puzzlereasoning

Tests an AI's ability to solve a simple but potentially confusing logic puzzle

GPT-5.1-Codex

GPT-5.1-Codex

Openai · Nov 2025text

Nothing here. The model returned empty. We stared at it for a while.

Try this prompt

Gemini 2.5 Pro (I/O Edition)

Gemini 2.5 Pro (I/O Edition)

Google · May 2025text

Let's break this down:

Sally is a girl.
Sally has 3 brothers.
These 3 brothers are all part of the same family.
Each brother shares the same sisters.
If one brother has 2 sisters, those 2 sisters are Sally and one other girl.

So, Sally has 1 sister.

Try this prompt

Vote

3 / 35

03

Math Misconception Testreasoning

Tests an AI's understanding of number representation

GPT-5.1-Codex

GPT-5.1-Codex

Openai · Nov 2025text

Nothing here. The model returned empty. We stared at it for a while.

Try this prompt

Gemini 2.5 Pro (I/O Edition)

Gemini 2.5 Pro (I/O Edition)

Google · May 2025text

Nothing here. The model returned empty. We stared at it for a while.

Try this prompt

Vote

4 / 35

04

Stochastic Consistency Testanalysis

Tests an AI's randomness and creativity

GPT-5.1-Codex

GPT-5.1-Codex

Openai · Nov 2025text

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? He was outstanding in his field.
Why don’t skeletons fight each other? They don’t have the guts.

All 5 jokes are unique.

Try this prompt

Gemini 2.5 Pro (I/O Edition)

Gemini 2.5 Pro (I/O Edition)

Google · May 2025text

Nothing here. The model returned empty. We stared at it for a while.

Try this prompt

Vote

5 / 35

05

SVG Layout Challengeimage generation

Tests an AI's ability to generate vector graphics

GPT-5.1-Codex

GPT-5.1-Codex

Openai · Nov 2025svg

Try this prompt

Gemini 2.5 Pro (I/O Edition)

Gemini 2.5 Pro (I/O Edition)

Google · May 2025svg

Nothing here. The model returned empty. We stared at it for a while.

Try this prompt

Vote

6 / 35

06

Xbox Controller SVG Artimage generation

Tests an AI's ability to create detailed SVG illustrations of gaming hardware

GPT-5.1-Codex

GPT-5.1-Codex

Openai · Nov 2025svg

Nothing here. The model returned empty. We stared at it for a while.

Try this prompt

Gemini 2.5 Pro (I/O Edition)

Gemini 2.5 Pro (I/O Edition)

Google · May 2025svg

Nothing here. The model returned empty. We stared at it for a while.

Try this prompt

Vote

Sponsored

7 / 35

07

Generate a Stand-Up Routineconversation

Tests an AI's humor and creative writing ability

GPT-5.1-Codex

GPT-5.1-Codex

Openai · Nov 2025text

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. I have a mixer that doesn’t fit in a drawer, I pay my taxes, and I buy the premium paper towels.”

Speaking of adult purchases, I recently spent way too much time comparing dishwasher pods. I’m reading the back trying to figure out if my dishes need “lemon zest technology” or “extra cascading action,” and the whole time I’m thinking, “My grandparents washed dishes in a bucket after walking uphill both ways, and here I am needing a second opinion on soap.” I called my mom to ask if she had any tips, and she just laughed and said, “Get plates you don’t mind being slightly dirty.” That’s wisdom.

And the gym—I don’t know why I keep trying. It’s just a place where I pay money to feel guilty for not going. The treadmill always looks at me like, “I know what you did last summer, and it was not cardio.” The last time I went, a trainer asked my “fitness goals.” I said, “Avoid eye contact with people who run marathons.” He wrote it down like, “Okay, feasible.” Then he asked about my diet. I told him I eat in a way that keeps me alive, but not well enough for Instagram. Apparently, that’s not a plan.

You ever notice how everything has a monthly subscription now? Music, TV, meal kits, meditation apps—there’s probably a subscription to remind me I have too many subscriptions. I signed up for one of those meditation apps, and now I stress about not having time to meditate. The notifications are like, “Take a deep breath.” I’m like, “I would, but I’m busy ignoring your other notifications.”

Dating is weird too. We’ve got apps that can tell you your soulmate is 3.7 miles away, but they can’t tell you whether that person knows how to use a microwave without burning water. You’ll be matching with someone based on your shared love of hiking and tacos, but their profile photo is them holding a fish. Why is every photo a fish? Are we dating humans or trying to start an aquarium? I never know what the fish is supposed to represent. “Look, I can provide.” Provide what? Mercury poisoning?

I tried a cooking class thinking I’d learn something practical, but instead it was mostly people “connecting with their culinary journey.” Meanwhile, I’m in the corner burning shallots and asking if it’s okay to use scissors on herbs. The instructor told us to “cook with intention,” and I’m like, “My intention is to avoid food poisoning.”

Anyway, thanks for listening. I gotta get home before my mixer feels neglected.

Try this prompt

Gemini 2.5 Pro (I/O Edition)

Gemini 2.5 Pro (I/O Edition)

Google · May 2025text

Nothing here. The model returned empty. We stared at it for a while.

Try this prompt

Vote

8 / 35

08

Realistic AI Interviewconversation

Tests an AI's ability to simulate personalities and predict future trends

GPT-5.1-Codex

GPT-5.1-Codex

Openai · Nov 2025text

Nothing here. The model returned empty. We stared at it for a while.

Try this prompt

Gemini 2.5 Pro (I/O Edition)

Gemini 2.5 Pro (I/O Edition)

Google · May 2025text

Nothing here. The model returned empty. We stared at it for a while.

Try this prompt

Vote

9 / 35

09

Satirical Fake News Headlineconversation

Tests an AI's humor and understanding of current events

GPT-5.1-Codex

GPT-5.1-Codex

Openai · Nov 2025text

Nothing here. The model returned empty. We stared at it for a while.

Try this prompt

Gemini 2.5 Pro (I/O Edition)

Gemini 2.5 Pro (I/O Edition)

Google · May 2025text

Nothing here. The model returned empty. We stared at it for a while.

Try this prompt

Vote

10 / 35

10

Minimalist Landing Pageweb design

Tests an AI's ability to generate a complete, working landing page

GPT-5.1-Codex

GPT-5.1-Codex

Openai · Nov 2025website

Try this prompt

Gemini 2.5 Pro (I/O Edition)

Gemini 2.5 Pro (I/O Edition)

Google · May 2025website

Try this prompt

Vote

11 / 35

11

Pokémon Battle UI Recreationweb design

Recreate an interactive, nostalgic Pokémon battle UI in a single HTML file.

GPT-5.1-Codex

GPT-5.1-Codex

Openai · Nov 2025website

Nothing here. The model returned empty. We stared at it for a while.

Try this prompt

Gemini 2.5 Pro (I/O Edition)

Gemini 2.5 Pro (I/O Edition)

Google · May 2025website

Nothing here. The model returned empty. We stared at it for a while.

Try this prompt

Vote

12 / 35

12

Mario Level UI Recreationweb design

Recreate an interactive, classic Mario level in a single HTML file.

GPT-5.1-Codex

GPT-5.1-Codex

Openai · Nov 2025website

Nothing here. The model returned empty. We stared at it for a while.

Try this prompt

Gemini 2.5 Pro (I/O Edition)

Gemini 2.5 Pro (I/O Edition)

Google · May 2025website

Try this prompt

Vote

This matchup has more rounds

23+ 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