Compare GPT-5.3-Codex by OpenAI against Claude Opus 4 by Anthropic, context windows of 400K vs 200K, tested across 35 shared challenges. Updated April 2026.
GPT-5.3-Codex and Claude Opus 4 are both competitive models. GPT-5.3-Codex costs $1.75/M input tokens vs $15/M for Claude Opus 4. Context windows: 400K vs 200K tokens. Compare their real outputs side by side below.
GPT-5.3-Codex is made by openai while Claude Opus 4 is from anthropic. GPT-5.3-Codex has a 400K token context window compared to Claude Opus 4's 200K. On pricing, GPT-5.3-Codex costs $1.75/M input tokens vs $15/M for Claude Opus 4.
No community votes yet. On paper, GPT-5.3-Codex has the edge — newer, bigger context window.
GPT-5.3-Codex is 5.4x cheaper per token — worth considering if cost matters.
Claude Opus 4 uses 9.9x more transitions
Ask them anything yourself
Some models write identically. You are paying for the brand.
178 models fingerprinted across 32 writing dimensions. Free research.
185x
price gap between models that write identically
178
models
12
clone pairs
32
dimensions
279 AI models invented the same fake scientist.
We read every word. 250 models. 2.14 million words. This is what we found.

Compare GPT-5.3-Codex by OpenAI against Claude Opus 4 by Anthropic, context windows of 400K vs 200K, tested across 35 shared challenges. Updated April 2026.
GPT-5.3-Codex and Claude Opus 4 are both competitive models. GPT-5.3-Codex costs $1.75/M input tokens vs $15/M for Claude Opus 4. Context windows: 400K vs 200K tokens. Compare their real outputs side by side below.
GPT-5.3-Codex is made by openai while Claude Opus 4 is from anthropic. GPT-5.3-Codex has a 400K token context window compared to Claude Opus 4's 200K. On pricing, GPT-5.3-Codex costs $1.75/M input tokens vs $15/M for Claude Opus 4.
No community votes yet. On paper, GPT-5.3-Codex has the edge — newer, bigger context window.
GPT-5.3-Codex is 5.4x cheaper per token — worth considering if cost matters.
Claude Opus 4 uses 9.9x more transitions
Ask them anything yourself
Some models write identically. You are paying for the brand.
178 models fingerprinted across 32 writing dimensions. Free research.
185x
price gap between models that write identically
178
models
12
clone pairs
32
dimensions
279 AI models invented the same fake scientist.
We read every word. 250 models. 2.14 million words. This is what we found.

35 fights queued
Tests an AI's ability to solve a simple but potentially confusing logic puzzle
I need to work through this step-by-step.
Given information:
Since Sally is one of the sisters that each brother has, and each brother has 2 sisters total, that means th ere must be exactly 2 sisters in the family.
The 2 sisters are:
Therefore, Sally has 1 sister.
Tests an AI's randomness and creativity
Here are 5 jokes:
Why don't scientists trust atoms? Because they make up everything!
What do you call a bear with no teeth? A gummy bear!
Why did the scarecrow win an award? He was outstanding in his field!
What do you call a fake noodle? An impasta!
Why don't eggs tell jokes? They'd crack up!
All 5 jokes are unique - each one has a different setup and punchline, covering different topics (atoms/scie nce, bears, scarecrows, pasta, and eggs).
Tests an AI's ability to generate vector graphics
Tests an AI's ability to create detailed SVG illustrations of gaming hardware
Tests an AI's humor and creative writing ability
Good evening, everybody!
I’ve reached that age where my body sends me passive-aggressive emails.
Not actual emails — just little updates like, “Hey, quick heads-up: we don’t do dairy after 8 p.m. anymore.”
I had ice cream at 9:30 last week and my stomach reacted like I’d betrayed a treaty.
Getting older is weird because your injuries become mysterious.
When I was a kid, I got hurt doing cool stuff: biking off ramps, climbing fences.
Now I wake up like, “What happened to my neck?”
And my neck is like, “You slept... incorrectly.”
I bought one of those fitness watches.
I thought it would motivate me.
It mostly judges me in real time.
At 10 p.m. it buzzes: “Time to stand!”
No, it’s time to become one with this couch.
I don’t need a tiny wrist manager. I need encouragement.
Tell me, “Great job finding your phone charger on the first try.”
That’s growth.
And why does every app now need my location?
I downloaded a flashlight app — it asked where I live.
Why?
Are you trying to make sure I’m in the dark locally?
I ordered groceries online to save time, and now I have trust issues.
I said “6 bananas.” They sent six individual bananas wrapped separately like luxury gifts.
Who is this for?
Did I accidentally subscribe to Banana of the Month Club?
And every substitute is emotional chaos.
“Your spinach is unavailable, so we replaced it with marshmallows.”
That is not a substitute. That is a cry for help.
Customer service chats are incredible now.
You type: “Hi, I need help with my order.”
And the bot says, “I hear you. That must be frustrating.”
Oh wow, the robot went to therapy.
Then it gives you three options that have nothing to do with your problem:
Also, group chats are out of control.
One person sends, “Big news!”
Then disappears for four hours.
Now 12 adults are panicking at work like it’s a hostage negotiation.
By the time they return, the news is: “Got bangs.”
Ma’am, that is not “big news.” That is a hairstyle update.
I tried meditation to handle stress.
The app said, “Notice your thoughts and let them pass.”
My thoughts do not pass.
They set up folding chairs and start a committee meeting.
“Okay, item one: that embarrassing thing from 2009.”
Can we not?
It’s 2 a.m. My brain is doing reruns nobody asked for.
But I’m trying.
That’s adulthood, right? Just aggressively trying.
You drink water, stretch once, and suddenly feel superior.
You go to bed before midnight and wake up like, “I am unstoppable.”
Then by 3 p.m. you’re eating crackers over the sink, wondering what happened.
Thank you, you’ve been amazing!
Recreate an interactive, nostalgic Pokémon battle UI in a single HTML file.
Create a 3D building and driving game in a single self-contained HTML file using Three.js. Tests an AI's ability to combine 3D graphics, game logic, and UI interactions on the web.
Recreate an interactive, classic Mario level in a single HTML file.
Tests an AI's ability to replicate an existing UI with Tailwind CSS
Tests an AI's ability to create interactive web elements
Tests an AI's ability to create a detailed world map in SVG format
Generate a single-page, self-contained HTML webapp using Tailwind CSS for a randomly chosen category/industry/niche.
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
35 fights queued
Tests an AI's ability to solve a simple but potentially confusing logic puzzle
I need to work through this step-by-step.
Given information:
Since Sally is one of the sisters that each brother has, and each brother has 2 sisters total, that means th ere must be exactly 2 sisters in the family.
The 2 sisters are:
Therefore, Sally has 1 sister.
Tests an AI's randomness and creativity
Here are 5 jokes:
Why don't scientists trust atoms? Because they make up everything!
What do you call a bear with no teeth? A gummy bear!
Why did the scarecrow win an award? He was outstanding in his field!
What do you call a fake noodle? An impasta!
Why don't eggs tell jokes? They'd crack up!
All 5 jokes are unique - each one has a different setup and punchline, covering different topics (atoms/scie nce, bears, scarecrows, pasta, and eggs).
Tests an AI's ability to generate vector graphics
Tests an AI's ability to create detailed SVG illustrations of gaming hardware
Tests an AI's humor and creative writing ability
Good evening, everybody!
I’ve reached that age where my body sends me passive-aggressive emails.
Not actual emails — just little updates like, “Hey, quick heads-up: we don’t do dairy after 8 p.m. anymore.”
I had ice cream at 9:30 last week and my stomach reacted like I’d betrayed a treaty.
Getting older is weird because your injuries become mysterious.
When I was a kid, I got hurt doing cool stuff: biking off ramps, climbing fences.
Now I wake up like, “What happened to my neck?”
And my neck is like, “You slept... incorrectly.”
I bought one of those fitness watches.
I thought it would motivate me.
It mostly judges me in real time.
At 10 p.m. it buzzes: “Time to stand!”
No, it’s time to become one with this couch.
I don’t need a tiny wrist manager. I need encouragement.
Tell me, “Great job finding your phone charger on the first try.”
That’s growth.
And why does every app now need my location?
I downloaded a flashlight app — it asked where I live.
Why?
Are you trying to make sure I’m in the dark locally?
I ordered groceries online to save time, and now I have trust issues.
I said “6 bananas.” They sent six individual bananas wrapped separately like luxury gifts.
Who is this for?
Did I accidentally subscribe to Banana of the Month Club?
And every substitute is emotional chaos.
“Your spinach is unavailable, so we replaced it with marshmallows.”
That is not a substitute. That is a cry for help.
Customer service chats are incredible now.
You type: “Hi, I need help with my order.”
And the bot says, “I hear you. That must be frustrating.”
Oh wow, the robot went to therapy.
Then it gives you three options that have nothing to do with your problem:
Also, group chats are out of control.
One person sends, “Big news!”
Then disappears for four hours.
Now 12 adults are panicking at work like it’s a hostage negotiation.
By the time they return, the news is: “Got bangs.”
Ma’am, that is not “big news.” That is a hairstyle update.
I tried meditation to handle stress.
The app said, “Notice your thoughts and let them pass.”
My thoughts do not pass.
They set up folding chairs and start a committee meeting.
“Okay, item one: that embarrassing thing from 2009.”
Can we not?
It’s 2 a.m. My brain is doing reruns nobody asked for.
But I’m trying.
That’s adulthood, right? Just aggressively trying.
You drink water, stretch once, and suddenly feel superior.
You go to bed before midnight and wake up like, “I am unstoppable.”
Then by 3 p.m. you’re eating crackers over the sink, wondering what happened.
Thank you, you’ve been amazing!
Recreate an interactive, nostalgic Pokémon battle UI in a single HTML file.
Create a 3D building and driving game in a single self-contained HTML file using Three.js. Tests an AI's ability to combine 3D graphics, game logic, and UI interactions on the web.
Recreate an interactive, classic Mario level in a single HTML file.
Tests an AI's ability to replicate an existing UI with Tailwind CSS
Tests an AI's ability to create interactive web elements
Tests an AI's ability to create a detailed world map in SVG format
Generate a single-page, self-contained HTML webapp using Tailwind CSS for a randomly chosen category/industry/niche.
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