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  5. GPT-6 LunavsGrok 4.5
Updated Sep 2026

GPT-6 LunavsGrok 4.5

GPT-6 Luna is cheaper than Grok 4.5 at $0.1/M vs $2/M input tokens.

GPT-6 Luna and Grok 4.5 compared across 20 shared prompts
SpecGPT-6 LunaGrok 4.5
Input price$0.1/M tokens$2/M tokens
Output price$0.5/M tokens$6/M tokens
Context window1.1M tokens500K tokens
WeightsClosedClosed
Free API (OpenRouter)NoNo
ReleasedSep 2026Jul 2026
Side by side

Same prompt, both answers

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

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 4.5212 words
Spellbound Spaghetti (savory) A quick, cozy tomato pasta that tastes like it took far more effort. Serves 2. 7 pantry ingredients 8 oz (225 g) dry pasta (spaghetti, penne, or whatever you have) 2 Tbsp olive oil (or any neutral oil) 1 (14–15 oz) can diced or crushed tomatoes 1 tsp garlic powder 1 tsp dried oregano (or…
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 4.51,578 words
Accelerated electronics from ~1920 would compress the digital and computational revolutions by roughly 20–30 years, reshaping WWII lethality and duration, advancing the Cold War into an earlier high-tech standoff, pulling the space race forward, creating an information-heavy economy by the 1950s–60s, and producing…
Read the full answer

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 4.51,791 words
All major clauses in this agreement are heavily one-sided and can be exploited against the Contractor. Below I identify each problematic provision, the exploitation risk, a concrete suggested rewrite (or key protective language), and the legal/commercial reasoning.
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Debug This Architecture

Here's the architecture for a real-time collaborative document editor (like Google Docs): **System Overview:** - Frontend: React SPA with…

GPT-6 Luna1,979 words
The main architectural risk is that the system treats collaborative editing as “write a value, then broadcast it.” That works poorly under concurrency, server failures, reconnects, and scale.
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Grok 4.51,572 words
Architecture Review: Real-Time Collaborative Document Editor This design has fundamental real-time and consistency problems. Several choices (client clocks, LWW, per-server WebSockets + DB polling, CDN-cached APIs, full HTML snapshots) will cause data loss, stale UI, and poor scale.
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Michelin Star Recipe Design

Design an innovative recipe for a multi-component dish worthy of a Michelin 3-star restaurant. The recipe should feature an unusual…

GPT-6 Luna1,249 words
Turbot, White Asparagus, Green Strawberry Kosho & Toasted-Hay Beurre Blanc A composed spring dish for four, built around an unusual pairing: tart green strawberry and toasted hay.
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Grok 4.51,266 words
Lunar Abyss Diver scallops · black garlic · white chocolate · black truffle · yuzu Conceptual Narrative The dish evokes a moonlit coastal forest where ocean and earth exchange secrets under tidal pull.
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Mini LBO Underwrite

You are underwriting a 5-year LBO for a private equity investment committee. Company (fictional): HarborTech Services (HTS) –…

GPT-6 Luna405 words
All figures in $m. Assumptions: annual Term Loan amortization is 1% of original principal ($4.8m); cash interest is based on beginning-of-year balances; Mezz PIK compounds annually.
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Grok 4.5533 words
HarborTech Services (HTS) – 5-Year LBO Underwriting Entry (end-FY2025 close) EV = 12.0x × $120m = $1,440m Fees = 2% × $1,440m = $28.8m Total uses = $1,468.8m Debt = 5.5x × $120m = $660m (TL $480m + Mezz $180m) Equity = $808.8m Cash = $0 Mandatory TL amort = 1% of original = $4.8m/yr.
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Our Verdict
GPT-6 Luna
GPT-6 Luna
Grok 4.5
Grok 4.5Runner-up

Not enough votes to call it. On the specs, GPT-6 Luna has the edge: newer, bigger context window.

GPT-6 Luna costs 12x 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
20× cheaper
Output
$0.50
12× cheaper
Grok 4.5
Input
$2.00
Output
$6.00

GPT-6 Luna is cheaper on both: 20× input, 12× 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 4.51 host
HostInOutContextUptime
xAI$2.00 in·$6.00 out·500k·99.3% 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 4.5 is developed by xAI. GPT-6 Luna has a 1.1M token context window vs Grok 4.5's 500K. 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 4.5 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 4.5 costs $2/M input tokens. GPT-6 Luna is $1.90/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 4.5 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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