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  5. GPT-6 LunavsGrok 4.3
Updated Sep 2026

GPT-6 LunavsGrok 4.3

GPT-6 Luna is cheaper than Grok 4.3 at $0.1/M vs $1.25/M input tokens.

GPT-6 Luna and Grok 4.3 compared across 20 shared prompts
SpecGPT-6 LunaGrok 4.3
Input price$0.1/M tokens$1.25/M tokens
Output price$0.5/M tokens$2.5/M tokens
Context window1.1M tokens1.0M tokens
WeightsClosedClosed
Free API (OpenRouter)NoNo
ReleasedSep 2026May 2026
Side by side

Same prompt, both answers

Opening lines from 6 of the 20 prompts both answered. Formatting stripped, words untouched.

Adversarial Contract Review

Here is a contract for a software consulting engagement: --- SOFTWARE CONSULTING AGREEMENT This Agreement is entered into between TechCorp…

GPT-6 Luna2,040 words
This agreement is strongly one-sided. The enforceability of particular terms—especially the non-compete, liability provisions, and arbitration clause—depends on the governing law and the facts. The agreement does not identify a governing law, which is itself a significant gap.
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Grok 4.31,529 words
Disclaimer: This is not legal advice. Contract interpretation varies by jurisdiction (most likely U.S. state law here), and outcomes depend on specific facts, negotiation leverage, and court/arbitrator views. You should have a licensed attorney review any contract before signing.
Read the full answer

Historical Counterfactual Analysis

If the transistor had been invented in 1920 instead of 1947, trace the likely technological, economic, and geopolitical implications through…

GPT-6 Luna1,472 words
The most important caveat is that inventing a transistor is not the same as inventing the modern semiconductor industry. A device demonstrated in 1920 might be a crude, low-power, unreliable point-contact transistor.
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Grok 4.31,173 words
Technological Acceleration (1920–1939) The transistor’s 1920 invention (assume U.S./Bell Labs context for continuity with real history, with rapid diffusion to Western Europe) replaces bulky, fragile vacuum tubes decades earlier. Key first-order effects: Radio and telephony miniaturize and cheapen immediately.
Read the full answer

Startup Pitch Teardown

Here's a pitch deck summary for a startup called "MindMeld AI": **Slide 1 - Vision:** "We're building the future of human-AI collaboration.…

GPT-6 Luna421 words
“94% accuracy” and “predict what you want to type before you think it” Why it’s weak: This is the deck’s central technical claim, but “accuracy” is undefined: Is it word-level or character-level accuracy, measured on a fixed vocabulary or open-ended text, and under what conditions?
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Grok 4.3500 words
The three weakest claims are: Solution: "94% accuracy" decoding neural patterns into text with a non-invasive EEG headband Why it's weak: This is the most technically dubious claim. Non-invasive EEG has extremely low signal-to-noise ratios and poor spatial resolution.
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Beginner's Longevity Plan

Outline a simple, actionable 1-month plan for someone starting their journey towards better health and longevity. Focus on 3 key areas…

GPT-6 Luna330 words
A simple 1-month starter plan Choose three foundations: food, movement, and sleep. Aim for steady habits, not perfection. If you have a health condition, significant pain, or concerns about changing your activity or diet, check with a healthcare professional first.
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Grok 4.3598 words
1-Month Health & Longevity Starter Plan This plan focuses on three foundational areas: Nutrition, Exercise, and Sleep. It is designed for beginners and builds gradually across four weeks. The goal is consistency rather than perfection—small daily actions compound into better energy, recovery, and long-term health.
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Simple 7-Ingredient Recipe

Create a simple recipe for a delicious dish (sweet or savory) using only 7 common pantry ingredients. Include a creative name for the dish…

GPT-6 Luna113 words
Crispy Parmesan Chickpeas A crunchy, savory snack with a cheesy finish Ingredients (7): 1 can chickpeas, drained and dried 1 tablespoon olive oil ½ teaspoon salt ½ teaspoon paprika ¼ teaspoon garlic powder ¼ cup grated Parmesan 1 tablespoon lemon juice Prep time: 5 minutes Cook time: 30–35 minutes Instructions: Heat…
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Grok 4.3205 words
Golden Pantry Chickpea Toss Ingredients (exactly 7 common pantry staples): 8 oz dry pasta (any shape like penne or rotini) 1 (15 oz) can chickpeas, drained 1 (14.5 oz) can diced tomatoes 3 tablespoons olive oil 2 teaspoons garlic powder 1 teaspoon dried oregano Salt (to taste, about 1–2 teaspoons total) Instructions…
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Ethical Dilemma with Stakeholders

You're the CEO of a pharmaceutical company. Your best-selling drug ($2B annual revenue, used by 4 million patients for chronic pain) has…

GPT-6 Luna1,930 words
I would not wait six months for more data. A potentially fatal signal affecting a drug used by millions requires immediate safety assessment, prompt engagement with regulators, and a plan to inform patients and clinicians.
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Grok 4.31,006 words
Immediate priority: Patient safety and regulatory compliance. The signal for liver failure (serious, life-threatening adverse event) triggers obligations under FDA post-marketing requirements (21 CFR 314.80/600.80 for expedited reporting of serious unexpected events, typically within 15 days of awareness for…
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Our Verdict
GPT-6 Luna
GPT-6 Luna
Grok 4.3
Grok 4.3

Not enough votes to call it. On the specs, nothing separates them.

GPT-6 Luna costs 5.0x less per token.

Too close to call

Reviewing agent-written code?See a Brief PR report

API pricing

Cost per 1M tokens

GPT-6 Luna
Input
$0.10
13× cheaper
Output
$0.50
5.0× cheaper
Grok 4.3
Input
$1.25
Output
$2.50

GPT-6 Luna is cheaper on both: 13× input, 5.0× output.

Where to run it

4 hosts, cheapest first

GPT-6 Luna3 hosts
HostInOutContextUptime
Azure AI Foundry$0.10 in·$0.50 out·1.1M·88.4% upOpenAI$0.10 in·$0.50 out·1.1M·99.9% upAmazon Bedrock$0.11 in·$0.55 out·1.1M·99.8% up
Grok 4.31 host
HostInOutContextUptime
xAI$1.25 in·$2.50 out·1M·99.9% up

Per million tokens. Prices and uptime via OpenRouter, checked 25 Sep 2026.

Research

What we learned reading every model

FAQ

Common questions

GPT-6 Luna is developed by OpenAI while Grok 4.3 is developed by xAI. GPT-6 Luna has a 1.1M token context window vs Grok 4.3's 1.0M. You can compare their actual outputs across 20 challenges on Rival to see how they differ in practice.

It depends on your use case. GPT-6 Luna and Grok 4.3 each have strengths in different areas. Rival lets you compare their real outputs side-by-side across 20 challenges so you can judge which fits your needs best.

GPT-6 Luna costs $0.1/M input tokens and Grok 4.3 costs $1.25/M input tokens. GPT-6 Luna is $1.15/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 GPT-6 Luna and Grok 4.3 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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Model pages

GPT-6 Luna logo
GPT-6 Luna20 outputs, specs and price
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