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  5. GPT-5.1 Codex MaxvsGPT-6 Luna
Updated Sep 2026

GPT-5.1 Codex MaxvsGPT-6 Luna

GPT-6 Luna is the newer model, released after GPT-5.1 Codex Max.

GPT-5.1 Codex Max and GPT-6 Luna compared across 20 shared prompts
SpecGPT-5.1 Codex MaxGPT-6 Luna
Input price—$0.1/M tokens
Output price—$0.5/M tokens
Context window—1.1M tokens
WeightsClosedClosed
Free API (OpenRouter)NoNo
ReleasedDec 2025Sep 2026
Side by side

Same prompt, both answers

Opening lines from 3 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-5.1 Codex Max175 words
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…
Read the full answer
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…
Read the full answer

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-5.1 Codex Max386 words
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.
Read the full answer
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.
Read the full answer

Mini LBO Underwrite

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

GPT-5.1 Codex Max192 words
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.
Read the full answer
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.
Read the full answer
Our Verdict
GPT-5.1 Codex Max
GPT-5.1 Codex Max
GPT-6 Luna
GPT-6 Luna

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

Too close to call

Reviewing agent-written code?See a Brief PR report

API pricing

Cost per 1M tokens

GPT-5.1 Codex Max
Input
—
Output
—
GPT-6 Luna
Input
$0.10
Output
$0.50
Where to run it

4 hosts, cheapest first

GPT-5.1 Codex Max1 host
HostInOutContextUptime
Azure AI Foundry$1.25 in·$10.00 out·400k·100% up
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

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

Research

What we learned reading every model

FAQ

Common questions

Both are developed by OpenAI but target different use cases. 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-5.1 Codex Max and GPT-6 Luna 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.

This page shows a side-by-side comparison of GPT-5.1 Codex Max and GPT-6 Luna 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.

Keep exploring

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GPT-6 Luna logoGPT-6 Sol Pro logo
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Same lab, same size, long tail

GPT-5.1 Codex Max logoGPT-6 Sol Pro logo
GPT-5.1 Codex Max vs GPT-6 Sol ProSame lab
GPT-5.1 Codex Max logoGPT-6 Sol logo
GPT-5.1 Codex Max vs GPT-6 SolSame lab
GPT-6 Luna logoGPT-6 Luna Pro logo
GPT-6 Luna vs GPT-6 Luna ProSame lab
GPT-6 Luna logoGPT-6 Sol logo
GPT-6 Luna vs GPT-6 SolSame lab
GPT-5.1 Codex Max logoLing 2.6 Flash logo
GPT-5.1 Codex Max vs Ling 2.6 FlashNew provider
GPT-5.1 Codex Max logoLing 3.0 Flash logo
GPT-5.1 Codex Max vs Ling 3.0 FlashSame size
GPT-5.1 Codex Max logoLing 3.0 Flash Fin (free) logo
GPT-5.1 Codex Max vs Ling 3.0 Flash Fin (free)New provider
GPT-5.1 Codex Max logoLing 3.0 Flash Sante (free) logo
GPT-5.1 Codex Max vs Ling 3.0 Flash Sante (free)New provider

Model pages

GPT-5.1 Codex Max logo
GPT-5.1 Codex Max53 outputs, specs and price
GPT-6 Luna logo
GPT-6 Luna20 outputs, specs and price
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