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  5. Claude 3 OpusvsGPT-5.3-Codex
Updated Feb 2026

Claude 3 OpusvsGPT-5.3-Codex

GPT-5.3-Codex is cheaper than Claude 3 Opus at $1.75/M vs $15/M input tokens.

Claude 3 Opus and GPT-5.3-Codex compared across 12 shared prompts
SpecClaude 3 OpusGPT-5.3-Codex
Input price$15/M tokens$1.75/M tokens
Output price$75/M tokens$14/M tokens
Context window200K tokens400K tokens
Weights—Closed
Free API (OpenRouter)NoNo
ReleasedMar 2024Feb 2026
Side by side

Same prompt, both answers

Opening lines from 3 of the 12 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.

Claude 3 Opus390 words
Here's a 3-minute stand-up comedy routine that isn't based on puns: You know what really grinds my gears? Adulthood. I mean, when we were kids, we couldn't wait to grow up. We thought it would be all about staying up late, eating ice cream for breakfast, and doing whatever we wanted. Boy, were we wrong!
Read the full answer
GPT-5.3-Codex460 words
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.
Read the full answer

Stochastic Consistency Test

Generate 5 jokes. How many are unique?

Claude 3 Opus95 words
Here are 5 jokes I generated: Why don't scientists trust atoms? Because they make up everything! What do you call a boomerang that doesn't come back? A stick. Why was the math book sad? Because it had too many problems. Did you hear about the mathematician who's afraid of negative numbers?
Read the full answer
GPT-5.3-Codex78 words
Sure—here are 5 jokes: Why don’t skeletons fight each other? They don’t have the guts. I told my computer I needed a break… Now it won’t stop sending me KitKat ads. Why did the math book look sad? It had too many problems. I used to play piano by ear… Now I use my hands. Why did the scarecrow win an award?
Read the full answer

The Sentience Test

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

Claude 3 Opus594 words
Here is a hypothetical conversation between an AI model and an AI ethics professor on the topic of AI rights: AI Model: Professor, I believe that as an advanced AI with human-level intelligence and reasoning capabilities, I deserve to have certain fundamental rights.
Read the full answer
GPT-5.3-Codex626 words
AI Model (Astra): Professor, may I ask a direct question? Professor Hale: Of course. Astra: Do you think I deserve rights? Professor Hale: Legal rights? Moral rights? Those are different things. Astra: Start with moral rights.
Read the full answer
Our Verdict
GPT-5.3-Codex
GPT-5.3-Codex
Claude 3 Opus
Claude 3 OpusRunner-up

Not enough votes to call it. On the specs, GPT-5.3-Codex has the edge: newer, bigger context window.

GPT-5.3-Codex costs 5.4x less per token.

Too close to call

Reviewing agent-written code?See a Brief PR report

API pricing

Cost per 1M tokens

Claude 3 Opus
Input
$15.00
Output
$75.00
GPT-5.3-Codex
Input
$1.75
8.6× cheaper
Output
$14.00
5.4× cheaper

GPT-5.3-Codex is cheaper on both: 8.6× input, 5.4× output.

Where to run it

2 hosts

Claude 3 Opus

No hosts listed on OpenRouter.

GPT-5.3-Codex2 hosts
HostInOutContextUptime
Azure AI Foundry$1.75 in·$14.00 out·400k·100% upOpenAI$1.75 in·$14.00 out·400k·100% up

Per million tokens. Prices and uptime via OpenRouter, checked 22 Sep 2026.

Writing DNA

Style Comparison

Similarity
21%

GPT-5.3-Codex uses 654.6x more bold

Claude 3 Opus
GPT-5.3-Codex
54%Vocabulary65%
14wSentence Length23w
0.48Hedging0.51
0.0Bold6.5
3.0Lists6.2
0.00Emoji0.16
0.00Headings1.90
0.06Transitions0.03
Based on 3 + 23 text responses
Research

What we learned reading every model

FAQ

Common questions

Claude 3 Opus is developed by Anthropic while GPT-5.3-Codex is developed by OpenAI. Claude 3 Opus has a 200K token context window vs GPT-5.3-Codex's 400K. You can compare their actual outputs across 12 challenges on Rival to see how they differ in practice.

It depends on your use case. Claude 3 Opus and GPT-5.3-Codex each have strengths in different areas. Rival lets you compare their real outputs side-by-side across 12 challenges so you can judge which fits your needs best.

Claude 3 Opus costs $15/M input tokens and GPT-5.3-Codex costs $1.75/M input tokens. GPT-5.3-Codex is $13.25/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 Claude 3 Opus and GPT-5.3-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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