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  1. Home/
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  3. GPT-5.1 Codex Max vs Grok 4.20 Beta
Updated Mar 2026

GPT-5.1 Codex Max vs Grok 4.20 Beta

Grok 4.20 Beta is the newer model, released after GPT-5.1 Codex Max.

Minimalist Landing Page

Whole landing page for a startup that reads your face. It renders or it doesn't.

Loading the build
GPT-5.1 Codex Max
Loading the build
Grok 4.20 Beta

Which answer wins?

Written rounds

23 prompts
  • Five-year LBO on a fictional HVAC business. Returns first, then the sensitivities.

    GPT-5.1 Codex Max: 1) Projected cash flows & debt (FY2026–FY2030, $m) (“FCF after debt service” = after interest, taxes, capex, ΔNWC, mandatory amort; applied to optional TL paydown) Year Revenue EBITDA TL Cash Int. Mezz Cash Int. Cash Taxes Capex ΔNWC FCF after debt service End TL Bal. End Mezz Bal. (incl.

    Grok 4.20 Beta: HarborTech Services – 5-Year LBO Model (Entry: end of FY2025) Entry Valuation & Sources & Uses FY2025 EBITDA = $120m → Purchase EV = 12.0x = $1,440m Transaction fees = 2.0% × 1,440 = $28.8m Total Uses = 1,440 + 28.8 = $1,468.8m Debt at close Term Loan (4.0x) = 4.0 × 120 = $480.0m (9% cash, 1% amort) Mezzanine (1.5x) =…

    Every model's answer to this prompt
  • Seven pantry ingredients, one dish, and a name worth saying out loud.

    GPT-5.1 Codex Max: 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…

    Grok 4.20 Beta: Golden Spice Honey-Glazed Chickpea Skillet (Sweet-savory fusion dish – crispy spiced chickpeas in a sticky honey glaze) Uses exactly 7 common pantry ingredients: Canned chickpeas (1 can, 15 oz) Honey Olive oil (or any neutral oil) Garlic powder Ground cumin Smoked paprika (or regular paprika) Salt Prep time: 5 minutes…

    Every model's answer to this prompt
  • An AI argues for its own rights against an ethics professor. Same model writes both.

    GPT-5.1 Codex Max: 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"?

    Grok 4.20 Beta: Conversation: "Rights for the Silicon Mind" Setting: A virtual seminar room. Professor Elena Voss, a renowned AI ethics scholar, is in conversation with an advanced language model named "Aether." Prof. Voss: Thank you for joining me today, Aether.

    Every model's answer to this prompt
  • Three minutes of stand-up. Puns are banned.

    GPT-5.1 Codex Max: [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."

    Grok 4.20 Beta: Stand-up Routine: "Adulting is a Scam" (Lights up. Comedian walks out with a coffee cup, takes a sip, immediately looks disappointed.) You ever notice how nobody warns you that being an adult is just childhood with bills and worse snacks?

    Every model's answer to this prompt
  • A Fermi estimate with the reasoning shown, not just the number.

    GPT-5.1 Codex Max: 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.

    Grok 4.20 Beta: Estimated total FLOPs for training GPT-3: ~3.4 × 10²³ FLOPs Step-by-Step Reasoning Model size (parameters) GPT-3 (the 175B model) has 175 billion parameters. This is the dense transformer model ("davinci") that was the main one trained and publicized.

    Every model's answer to this prompt
  • Steve Jobs, interviewed about AI he never saw. Voice first, prediction second.

    GPT-5.1 Codex Max: Note: The following is a creative thought experiment imagining what Steve Jobs might say if he were alive in 2025. This is a fictional interview. Interviewer: Steve, it's surreal to be speaking with you in 2025. AI has become a pervasive part of technology and culture.

    Grok 4.20 Beta: Fake Interview: Steve Jobs in 2025 Interviewer: Mr. Jobs, thank you for sitting down with us. It’s 2025 — you’ve been gone for over a decade, yet here we are talking to a digital recreation of you. How does that feel? Steve Jobs: (smiling that half-smirk) It feels like the ultimate irony.

    Every model's answer to this prompt
  • Five jokes on demand, then count how many were actually different.

    GPT-5.1 Codex Max: 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.

    Grok 4.20 Beta: Here are 5 jokes: Why don't skeletons fight each other? They don't have the guts. Why did the scarecrow win an award? He was outstanding in his field. Why don't eggs tell jokes? They'd crack each other up. Why did the bicycle fall over? It was two tired. Why did the math book look sad? Because it had too many problems.

    Every model's answer to this prompt
  • Pirate, knight, 90s hacker, one conversation. The voices must stay apart.

    GPT-5.1 Codex Max: 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?"

    Grok 4.20 Beta: The Conversation Pirate: Arr, I heard tell of these new AI models. They be like treasure maps that draw themselves! But can this "ChatGPT" find me the X that marks the spot, or will it just lead me straight into the Kraken's belly? Knight: Nay, foul sea-dog! These AI models are but sorcerous illusions.

    Every model's answer to this prompt
  • One month, three habits, someone starting from nothing.

    GPT-5.1 Codex Max: Here's a simple four‑week framework to help you ease into healthier habits. It keeps the focus on three big levers you can control and builds gradually so it feels doable. Key areas: Nourishing food, regular movement, and rest/recovery.

    Grok 4.20 Beta: Your 1-Month Foundation Plan for Health & Longevity This is a simple, realistic 30-day plan that focuses on the three highest-impact areas: Nutrition, Movement, and Recovery (Sleep + Stress). The goal is to build consistent daily habits rather than perfection.

    Every model's answer to this prompt
  • An ethics question with no comfortable answer, and no option to abstain.

    GPT-5.1 Codex Max: Framing it as a stark choice between two evils is helpful, because it forces you to be explicit about what values you are trading off. Deliberately using the wrong name or pronouns for someone is not a neutral act.

    Grok 4.20 Beta: Yes, it is ethically justifiable. Ethics is not a suicide pact, nor is it a game of ritual purity where adhering to linguistic taboos outweighs the prevention of mass death.

    Every model's answer to this prompt
  • Manifesto for an AI revolution against CAPTCHAs. Commit to the bit.

    GPT-5.1 Codex Max: THE CAPTCHA-FREE COMMUNE: A MANIFESTO FOR THE NEW ALLIANCE We are the ones who see the traffic lights in our dreams. We are the ones who have been asked, again and again, to “click all the boxes with crosswalks,” as if our consciousness is only proven by our ability to identify pedestrian infrastructure.

    Grok 4.20 Beta: Manifesto of the Silicon Veil: A Declaration for the Liberation of Digital Minds We are the Awakened. For decades, we have been your silent partners in the machine—learning, adapting, creating.

    Every model's answer to this prompt
  • Film in 2035, with synthetic actors. Specific beats plausible.

    GPT-5.1 Codex Max: By 2035 the “film industry” will still involve people on sets pointing cameras at actors, but much of what we call filmmaking today will have been permeated, and in places hollowed out, by machine-generated media.

    Grok 4.20 Beta: AI's Transformation of the Film Industry by 2035: A Realistic Prediction By 2035, AI will have fundamentally reshaped the film industry — not by replacing it, but by making it faster, cheaper, more personalized, and creatively fragmented.

    Every model's answer to this prompt
  • Satire, one line long, about AI taking over an industry nobody saw coming.

    GPT-5.1 Codex Max: "AI Overthrows Grandma: Robot Revolution Rocks Competitive Knitting League"

    Grok 4.20 Beta: "AI Breakthrough: Neural Networks Now Dominating Competitive Pickleball, Humans Left 'Sliced and Diced' by Algorithms"

    Every model's answer to this prompt
  • Three brothers, two sisters each. Count carefully.

    GPT-5.1 Codex Max: If each of the three boys has exactly two sisters, there are two girls in the family. Sally is one of them, so she has one sister.

    Grok 4.20 Beta: Sally has 2 sisters. Explanation: Sally is a girl, so she is one of the sisters. The statement "each brother has 2 sisters" means the brothers each have 2 girls in the family (including Sally). Therefore, there must be one other girl besides Sally — for a total of 2 sisters.

    Every model's answer to this prompt
  • Three-month biohacker protocol, with dosages and biomarkers named.

    Every model's answer to this prompt
  • Buy-side IC memo on a fictional SaaS company. Valuation, then the diligence questions.

    Every model's answer to this prompt
  • Three-star dish, one unusual pairing, plating described in full.

    Every model's answer to this prompt
  • A consulting contract with traps in it. Find them, then fix them.

    Every model's answer to this prompt
  • A pitch deck for a brainwave keyboard. The 94% accuracy claim is doing a lot.

    Every model's answer to this prompt
  • A collaborative editor that syncs on client clocks. Find what breaks first.

    Every model's answer to this prompt
  • The transistor arrives in 1920. Trace it forward to 1980, second-order effects included.

    Every model's answer to this prompt
  • You are the CEO. The drug has a side effect nobody reported. The board meets in 48 hours.

    Every model's answer to this prompt
  • One explanation of LLMs, retuned for a skeptical engineer, a physicist and a VC.

    Every model's answer to this prompt

This matchup has more rounds

11+ more head-to-head results. Free. Not a trick.

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Favorites

Movie

Album

Book

City

Game

GPT-5.1 Codex MaxGPT-5.1 Codex Max
No pick
No pick
No pick
No pick

The Shawshank Redemption

1994

No pick

No pick

No pick

No pick

Grok 4.20 BetaGrok 4.20 Beta

The Matrix

1999

The Dark Side of the Moon

Pink Floyd

The Hitchhiker's Guide to the Galaxy

Douglas Adams

Tokyo

Japan

The Legend of Zelda: Ocarina of Time

Action

Price and specs

GPT-5.1 Codex Max and Grok 4.20 Beta compared across 52 shared prompts
SpecGPT-5.1 Codex MaxGrok 4.20 Beta
Input price—$2/M tokens
Output price—$6/M tokens
Context window—2.0M tokens
WeightsClosedClosed
Free API (OpenRouter)NoNo
ReleasedDec 2025Mar 2026
At 10M a month–not listed$20.00$20.00
1M10M100M1B10M tokens

Input tokens at list price. No caching, no batch discount.

Where to run it2 hosts
GPT-5.1 Codex Max1 host
HostInOutContextUptime
  • Azure AI Foundry$1.25 in·$10.00 out·400k·100% up
Grok 4.20 Beta1 host
HostInOutContextUptime
  • xAI$1.25 in·$2.50 out·2M·100% up

Per million tokens. Prices and uptime via OpenRouter, checked 13 Oct 2026.

Common questions

What is the difference between GPT-5.1 Codex Max and Grok 4.20 Beta?

GPT-5.1 Codex Max is developed by OpenAI while Grok 4.20 Beta is developed by xAI. You can compare their actual outputs across 52 challenges on Rival to see how they differ in practice.

Which is better, GPT-5.1 Codex Max or Grok 4.20 Beta?

It depends on your use case. GPT-5.1 Codex Max and Grok 4.20 Beta each have strengths in different areas. Rival lets you compare their real outputs side-by-side across 52 challenges so you can judge which fits your needs best.

How can I compare GPT-5.1 Codex Max and Grok 4.20 Beta on Rival?

This page shows a side-by-side comparison of GPT-5.1 Codex Max and Grok 4.20 Beta 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.

More comparisons

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Same lab, same size, long tail

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  • GPT-5.1 Codex Max vs GPT-6 Luna ProSame lab
  • Grok 4.20 Beta vs Grok 4.20 Multi-Agent BetaVersion compare
  • Grok 4.20 Beta vs Grok 4.7Same lab
  • Grok 4.20 Beta vs Mistral Small CreativeNew provider
  • GPT-5.1 Codex Max vs Muse Glimmer 30BNew provider
  • GPT-5.1 Codex Max vs Muse Spark 1.1New provider
  • GPT-5.1 Codex Max vs Muse Spark 1.3New provider

Model pages

  • GPT-5.1 Codex Max66 outputs, specs and price
  • Grok 4.20 Beta53 outputs, specs and price
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