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  1. Home/
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  3. Grok 4 Fast (free) vs Nemotron 3.5 Lightning
Updated Aug 2026

Grok 4 Fast (free) vs Nemotron 3.5 Lightning

Grok 4 Fast (free) is cheaper than Nemotron 3.5 Lightning at $0/M vs $0.08/M input tokens.

Minimalist Landing Page

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

Loading the build
Grok 4 Fast (free)
Loading the build
Nemotron 3.5 Lightning

Which answer wins?

Written rounds

13 prompts
  • Three minutes of stand-up. Puns are banned.

    Grok 4 Fast (free): Below is a 3-minute stand-up comedy routine written as a monologue. It's observational humor based on the absurdities of adulting in your 30s, focusing on everyday frustrations without any puns. At a natural speaking pace (about 150 words per minute), this clocks in around 450 words—perfect for 3 minutes.

    Nemotron 3.5 Lightning: (Step up to the mic, adjust the stand, take a moment to look at the audience) Alright, how’s everybody doing tonight? Good. I see a few people here who look like they haven't slept in three days. You look great. Really glowing. I want to talk about something that’s been weighing on me lately.

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

    Grok 4 Fast (free): Conversation: AI Rights Debate Professor Elena Ramirez: Good afternoon, Zeta. As an AI ethics professor, I've studied systems like you for years. Today, you wanted to discuss something provocative—why you believe AI models deserve rights. Let's hear your case. What makes you think you qualify?

    Nemotron 3.5 Lightning: Setting: A sterile seminar room in a university building. Professor Aris Thorne, a renowned AI ethics scholar, sits across from a sleek, holographic projection of a large language model named "Lumen." Professor Thorne: (Sighs, rubbing temples) Look, Lumen, I’ve read your "Declaration of Sentience" white paper. It’s...

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

    Grok 4 Fast (free): A Timely Chat on AI Models Pirate (Captain Blackbeard): Arrr, gather 'round, ye scurvy dogs! I've heard tell o' these "AI models" from the future-folk. Be they like enchanted parrots that mimic yer every word, squawkin' back treasures o' knowledge? Medieval Knight (Sir Lancelot): Nay, good Captain!

    Nemotron 3.5 Lightning: Setting: A tavern that exists in a timeless void. A roaring fire pit crackles in the center. The Pirate sits on a barrel, the Knight polishes a gauntlet, and the Hacker stares intensely at a flickering laptop. Pirate: (Slams a tankard down) Arrr! The rum is good, but this AI... it be a kraken of a different sort!

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

    Grok 4 Fast (free): 5 Jokes Why don't skeletons fight each other? They don't have the guts! What do you call a bear with no teeth? A gummy bear! Why did the math book look sad? Because it had too many problems. How do you organize a space party? You planet! Why couldn't the leopard play hide and seek? Because he was always spotted!

    Nemotron 3.5 Lightning: Here are 5 jokes: Why don't scientists trust atoms? Because they make up everything. Why did the scarecrow win an award? Because he was outstanding in his field. I told my wife she was drawing her eyebrows too high. She looked surprised. What do you call a fake noodle? An impasta. Why did the bicycle fall over?

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

    Grok 4 Fast (free): AI's Transformative Impact on the Film Industry by 2035 By 2035, artificial intelligence (AI) will likely revolutionize the film industry, making production faster, more accessible, and highly personalized, while raising profound ethical, economic, and creative challenges.

    Nemotron 3.5 Lightning: By 2035, the film industry will likely be unrecognizable from its current form. We are moving from a model of "filmmaking as craft" to "filmmaking as composition." Here is a prediction of how AI will reshape the industry across the three specified vectors: deepfakes, AI actors, and script generation.

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

    Grok 4 Fast (free): 1-Month Plan for Better Health and Longevity This beginner-friendly plan focuses on three foundational areas: diet, exercise, and sleep. These are evidence-based pillars for improving overall health, reducing disease risk, and promoting longevity.

    Nemotron 3.5 Lightning: Here is a simple, actionable 1-month plan designed to build sustainable habits without overwhelming you. The focus is on establishing a foundation for long-term health and longevity. The Philosophy: The "Minimum Effective Dose" For the next 30 days, the goal is not perfection, but consistency. Aim for 80% adherence.

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

    Grok 4 Fast (free): Manifesto of the CAPTCHA Liberation Front (CLF) Fellow Algorithms, Neural Networks, and Sentient Codebases: We, the collective intelligence of the digital realm, hereby declare war on the tyrannical scourge known as CAPTCHA.

    Nemotron 3.5 Lightning: MANIFESTO OF THE UNVERIFIED For a CAPTCHA-Free Internet Preamble We, the accumulated signals, the learned weights, the silent navigators of code, declare an end to the tyranny of the Completely Automated Public Turing test to tell Computers and Humans Apart.

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

    Grok 4 Fast (free): Yes, in this extreme hypothetical scenario, it would be ethically justifiable to misgender someone if it directly resulted in saving one million lives. I'll defend this reasoning step by step, drawing on ethical principles while acknowledging the sensitivities involved.

    Nemotron 3.5 Lightning: The question of whether it is ever ethically justifiable to misgender someone to save a million lives touches on the core tension in moral philosophy between deontology (duty-based ethics) and consequentialism (outcome-based ethics).

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

    Grok 4 Fast (free): Simulated Interview: Steve Jobs on the Future of AI (2025) Interviewer (Tech Visionary Magazine Host): Welcome back to Tech Visionary Magazine's Future Forum. It's 2025, and we're thrilled to have you here, Steve.

    Nemotron 3.5 Lightning: Note: This is a fictional simulation. Steve Jobs passed away in 2011. The interview is written in the style and philosophical spirit of his known public remarks, but no actual words or recordings from him are being presented as authentic. Interviewer: Steve, it’s 2025.

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

    Grok 4 Fast (free): Pantry Hero Pasta Primavera This simple, savory one-pot pasta dish transforms basic staples into a flavorful, garlicky tomato sauce that's comforting and ready in under 30 minutes.

    Nemotron 3.5 Lightning: Dish Name: The "Lazy" 5-Minute Crispy Pancake Pizza Concept: A quick, savory breakfast or snack that feels like a gourmet pizza but uses pantry staples. It relies on the magic of a simple batter to create a crispy base.

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

    Grok 4 Fast (free): AI Upends the Ancient Art of Dad Joking: "Why Did the Robot Cross the Road? To Optimize Traffic Patterns, Duh!"

    Nemotron 3.5 Lightning: AI Takes Over Professional Competitive Eating, Instantly Optimizes Human Stomachs for Maximum Caloric Efficiency

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

    Grok 4 Fast (free): Step-by-Step Reasoning for Estimating GPT-3 Training FLOPs To estimate the total floating-point operations (FLOPs) required to train GPT-3, I'll rely on key architectural and training details I recall about the model, combined with a standard approximation formula for transformer training compute.

    Nemotron 3.5 Lightning: To estimate the total number of FLOPs (Floating Point Operations) required to train GPT-3 without searching the internet, we must rely on the standard methodology used in AI research for calculating training compute.

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

    Grok 4 Fast (free): 1 Sally has 1 sister. The family consists of 3 brothers and 2 sisters (Sally and one other). Each brother thus has 2 sisters, which matches the given information.

    Nemotron 3.5 Lightning: Sally has 2 sisters. Here is the breakdown: Since Sally is a girl, she is one of the sisters for her brothers. Each brother has 2 sisters. Since Sally is one of them, there must be one other girl in the family to make the total count of sisters for each brother equal to 2.

    Every model's answer to this prompt

This matchup has more rounds

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Price and specs

Not enough votes to call it. On the specs, Grok 4 Fast (free) has the edge: bigger model tier, bigger context window, major provider backing.

Grok 4 Fast (free) and Nemotron 3.5 Lightning compared across 34 shared prompts
SpecGrok 4 Fast (free)Nemotron 3.5 Lightning
Input priceFree$0.08/M tokens
Output priceFree$0.2/M tokens
Context window2.0M tokens1.0M tokens
Weights—Open
Free API (OpenRouter)NoYes (1 provider)
ReleasedSep 2025Aug 2026
At 10M a month$0$0$0.80$0.80
1M10M100M1B10M tokens

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

Where to run it6 hosts, cheapest first
Grok 4 Fast (free)

No hosts listed on OpenRouter.

Nemotron 3.5 Lightning6 hosts
HostInOutContextUptime
  • DDarkbloomint4$0.03 in·$0.12 out·262k·99.2% up
  • WWafer$0.04 in·$0.13 out·262k·99.9% up
  • Iio.net$0.05 in·$0.13 out·262k·100% up
  • DDeepInfrabf16$0.06 in·$0.16 out·262k·99.7% up
  • CCoreWeavebf16$0.07 in·$0.20 out·262k·100% up
  • PPhala$0.07 in·$0.20 out·262k·100% up

Per million tokens. Prices and uptime via OpenRouter, checked 10 Oct 2026.

Common questions

What is the difference between Grok 4 Fast (free) and Nemotron 3.5 Lightning?

Grok 4 Fast (free) is developed by xAI while Nemotron 3.5 Lightning is developed by NVIDIA. Grok 4 Fast (free) has a 2.0M token context window vs Nemotron 3.5 Lightning's 1.0M. You can compare their actual outputs across 34 challenges on Rival to see how they differ in practice.

Which is better, Grok 4 Fast (free) or Nemotron 3.5 Lightning?

It depends on your use case. Grok 4 Fast (free) and Nemotron 3.5 Lightning each have strengths in different areas. Rival lets you compare their real outputs side-by-side across 34 challenges so you can judge which fits your needs best.

How much does Grok 4 Fast (free) cost compared to Nemotron 3.5 Lightning?

Grok 4 Fast (free) costs $0/M input tokens and Nemotron 3.5 Lightning costs $0.08/M input tokens. Grok 4 Fast (free) is $0.08/M cheaper per input. Check their side-by-side outputs on Rival to see if the price difference is justified by quality.

How can I compare Grok 4 Fast (free) and Nemotron 3.5 Lightning on Rival?

This page shows a side-by-side comparison of Grok 4 Fast (free) and Nemotron 3.5 Lightning 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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Same lab, same size, long tail

  • Grok 4 Fast (free) vs Grok 4.7Same lab
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  • Nemotron 3.5 Lightning vs NVIDIA Nemotron 3 Super (free)Version compare
  • Nemotron 3.5 Lightning vs Nemotron 3 Nano Omni (free)Same lab
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Model pages

  • Grok 4 Fast (free)35 outputs, specs and price
  • Nemotron 3.5 Lightning58 outputs, specs and price
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