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  5. GPT-5.6 LunavsGPT-6 Luna Pro
Updated Sep 2026

GPT-5.6 LunavsGPT-6 Luna Pro

GPT-6 Luna Pro is cheaper than GPT-5.6 Luna at $0.1/M vs $1/M input tokens.

GPT-5.6 Luna and GPT-6 Luna Pro compared across 20 shared prompts
SpecGPT-5.6 LunaGPT-6 Luna Pro
Input price$1/M tokens$0.1/M tokens
Output price$6/M tokens$0.5/M tokens
Context window1.1M tokens1.1M tokens
WeightsClosedClosed
Free API (OpenRouter)NoNo
ReleasedJul 2026Sep 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-5.6 Luna152 words
Sunset Pantry Pasta A savory, slightly spicy tomato-tuna pasta made with seven simple pantry ingredients. Ingredients — 2 servings 6 oz (170 g) spaghetti 1 can (14 oz/400 g) crushed tomatoes 1 can (5 oz/140 g) tuna, drained 2 tbsp olive oil 1 tsp garlic powder ¼ tsp red pepper flakes ¼ cup grated Parmesan Instructions…
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GPT-6 Luna Pro127 words
Golden Pantry Pancakes Fluffy, lightly sweet pancakes made with everyday staples. Makes: About 6 small pancakes Prep time: 5 minutes Cook time: 10 minutes Ingredients 1 cup all-purpose flour 1 cup milk 1 egg 2 tablespoons sugar 1 teaspoon baking powder ¼ teaspoon salt 2 tablespoons butter, melted (plus a little for the…
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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-5.6 Luna2,445 words
The architecture has several correctness, availability, security, and scaling risks. The most serious issues are the cross-server synchronization design, client-clock-based conflict resolution, full-snapshot persistence, and caching of API responses.
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GPT-6 Luna Pro1,906 words
The main architectural risk is that this design treats collaborative editing as ordinary “last write wins” data storage. It is not: edits need a well-defined order, reliable propagation, and a conflict model that preserves concurrent work.
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-5.6 Luna608 words
1-Month Beginner Plan for Better Health and Longevity Key principles Aim for consistency, not perfection. Start small enough that you can repeat it. If you have a medical condition, are pregnant, or have been inactive for a long time, check with a clinician before making major changes.
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GPT-6 Luna Pro327 words
A simple 1-month plan for better health and longevity Choose three foundations: eating well, moving regularly, and sleeping consistently. Aim for steady habits, not perfection. Diet: Make nourishing choices easier Week 1: Add one serving of fruit or vegetables to one meal each day.
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Adversarial Contract Review

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

GPT-5.6 Luna2,809 words
Below is a contractor-side risk review. Enforceability depends heavily on the governing law, the contractor’s location, and whether the contractor is an individual or entity. Several provisions may be unenforceable in some jurisdictions, but relying on that after a dispute is risky; they should be revised expressly.
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GPT-6 Luna Pro2,116 words
This agreement is heavily one-sided. Several terms let the Client expand the work, delay or deny payment, claim ownership of the Contractor’s existing materials, and expose the Contractor to potentially unlimited liability.
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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-5.6 Luna1,583 words
Turbot “Between Forest and Sea” Koji-cured turbot, fermented pear, coffee-kombu beurre blanc, smoked sunchoke, maitake, spruce, and buckwheat–nori tuile Serves 4 Concept This dish treats the turbot as a meeting point between two landscapes.
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GPT-6 Luna Pro1,215 words
Turbot, Sea Buckthorn, Mussel Beurre Blanc, and Celery-Root Silk Serves 4 A composed main course built around an unusual but harmonious pairing: briny mussel and turbot with intensely tart, apricot-like sea buckthorn.
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Explain Like I'm a Specific Expert

Explain how a large language model (like GPT or Claude) learns and generates text to each of these three audiences: 1. **An experienced…

GPT-5.6 Luna842 words
For an experienced software engineer A language model is trained much like an extremely large system for compressing and reconstructing text. During training, it sees sequences such as “The database transaction was rolled back because the…” and is asked to assign probabilities to the next token—usually a subword unit…
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GPT-6 Luna Pro892 words
For an experienced software engineer Think of a language model as a system trained to continue sequences: given a prefix of text, it assigns probabilities to possible next tokens (tokens are pieces of words, not necessarily whole words) and learns to make the observed continuation likely.
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Our Verdict
GPT-6 Luna Pro
GPT-6 Luna Pro
GPT-5.6 Luna
GPT-5.6 LunaRunner-up

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

GPT-6 Luna Pro 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-5.6 Luna
Input
$1.00
Output
$6.00
GPT-6 Luna Pro
Input
$0.10
10× cheaper
Output
$0.50
12× cheaper

GPT-6 Luna Pro is cheaper on both: 10× input, 12× output.

Where to run it

5 hosts, cheapest first

GPT-5.6 Luna3 hosts
HostInOutContextUptime
Azure AI Foundry$0.20 in·$1.20 out·1.1M·99.5% upOpenAI$0.20 in·$1.20 out·1.1M·99.9% upAmazon Bedrock$0.22 in·$1.32 out·1.1M·100% up
GPT-6 Luna Pro2 hosts
HostInOutContextUptime
Azure AI Foundry$0.10 in·$0.50 out·1.1M·98.6% upOpenAI$0.10 in·$0.50 out·1.1M·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

Both are developed by OpenAI but target different use cases. GPT-5.6 Luna has a 1.1M token context window vs GPT-6 Luna Pro'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-5.6 Luna and GPT-6 Luna Pro 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-5.6 Luna costs $1/M input tokens and GPT-6 Luna Pro costs $0.1/M input tokens. GPT-6 Luna Pro is $0.90/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-5.6 Luna and GPT-6 Luna Pro 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-5.6 Luna logo
GPT-5.6 Luna58 outputs, specs and price
GPT-6 Luna Pro logo
GPT-6 Luna Pro20 outputs, specs and price
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