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  5. GPT-5.1-CodexvsGPT-6 Luna
Updated Sep 2026

GPT-5.1-CodexvsGPT-6 Luna

GPT-6 Luna is cheaper than GPT-5.1-Codex at $0.1/M vs $1.25/M input tokens.

GPT-5.1-Codex and GPT-6 Luna compared across 20 shared prompts
SpecGPT-5.1-CodexGPT-6 Luna
Input price$1.25/M tokens$0.1/M tokens
Output price$10/M tokens$0.5/M tokens
Context window400K tokens1.1M tokens
WeightsClosedClosed
Free API (OpenRouter)NoNo
ReleasedNov 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-Codex117 words
Recipe: Cloud-Burst Cinnamon Oat Cups Ingredients (7 total): Rolled oats – 1 cup Honey – 2 tbsp Peanut butter (or any nut butter) – 3 tbsp Cinnamon – ½ tsp Vanilla extract – ½ tsp Dried cranberries (or raisins) – ¼ cup Pinch of salt Instructions: In a bowl, microwave peanut butter and honey for 20 seconds just to…
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-Codex492 words
Here’s a simple, beginner-friendly 1-month plan focused on three key areas—Nutrition, Movement, and Rest & Recovery—to kickstart better health and longevity. Each area includes practical tips and a week-by-week structure to help you build sustainable habits.
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

Advanced Investment Memo (IC Memo)

You are writing an internal investment committee memo for a long/short equity fund. Company (fictional): LedgerLift (ticker: LLLT) – B2B…

GPT-5.1-Codex253 words
LedgerLift (LLLT) – Investment Committee Memo Recommendation Call: Short 12‑month price target range: $30–$40 Two-sentence thesis: LedgerLift’s premium multiple (10x NTM EV/rev implied by spot) is predicated on sustaining >20% top-line growth, yet leading indicators—moderating NRR, heavy S&M spend, and mid-market…
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GPT-6 Luna896 words
LedgerLift (LLLT) — Investment Committee Memo Recommendation: Short 12-month price target: $28–$42 At $46, LedgerLift’s price implies continued strong growth and margin expansion; our DCF scenarios value the shares at approximately $17–$42, with the base case near $28.
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Our Verdict
GPT-5.1-Codex
GPT-5.1-Codex
GPT-6 Luna
GPT-6 Luna

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

GPT-6 Luna costs 20x less per token.

Too close to call

Reviewing agent-written code?See a Brief PR report

API pricing

Cost per 1M tokens

GPT-5.1-Codex
Input
$1.25
Output
$10.00
GPT-6 Luna
Input
$0.10
13× cheaper
Output
$0.50
20× cheaper

GPT-6 Luna is cheaper on both: 13× input, 20× output.

Where to run it

4 hosts, cheapest first

GPT-5.1-Codex1 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. GPT-5.1-Codex has a 400K token context window vs GPT-6 Luna's 1.1M. 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 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.

GPT-5.1-Codex costs $1.25/M input tokens and GPT-6 Luna costs $0.1/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-5.1-Codex 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.

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Model pages

GPT-5.1-Codex logo
GPT-5.1-Codex53 outputs, specs and price
GPT-6 Luna logo
GPT-6 Luna20 outputs, specs and price
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