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  5. GPT-5.6 Luna ProvsGPT-6 Sol
Updated Sep 2026

GPT-5.6 Luna ProvsGPT-6 Sol

GPT-5.6 Luna Pro is cheaper than GPT-6 Sol at $1/M vs $2/M input tokens.

GPT-5.6 Luna Pro and GPT-6 Sol compared across 20 shared prompts
SpecGPT-5.6 Luna ProGPT-6 Sol
Input price$1/M tokens$2/M tokens
Output price$6/M tokens$10/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.

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 Luna Pro3,332 words
Below are the major correctness, availability, security, and scaling problems in the design, together with concrete mitigations and their trade-offs. Cross-server WebSocket synchronization Problem: Updates are broadcast only to clients on the receiving server If Alice is connected to Server A and Bob to Server B…
Read the full answer
GPT-6 Sol1,130 words
The central flaw is that the system treats collaborative edits as independent writes to a document. They are not: edits need a shared ordering and a merge protocol. Adding API servers or read replicas will not fix that. Issue and failure mode Specific solution Trade-off Client-clock last-write-wins loses work.
Read the full answer

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 Luna Pro126 words
Pantry Stardust Peanut Butter Oat Cookies Prep time: 10 minutes Cook time: 10–12 minutes Makes: About 12 cookies Ingredients 1 cup rolled oats ½ cup all-purpose flour ½ cup peanut butter ½ cup granulated sugar 1 large egg ½ teaspoon baking soda ¼ teaspoon salt Instructions Preheat the oven to 350°F (175°C) and line a…
Read the full answer
GPT-6 Sol90 words
Smoky Sunset Chickpeas Prep: 5 minutes · Cook: 15 minutes · Serves: 2 Ingredients 1 can chickpeas, drained 1 can diced tomatoes 1 tablespoon olive oil 2 garlic cloves, minced 1 teaspoon dried oregano ½ teaspoon smoked paprika ½ teaspoon salt Instructions Heat the olive oil in a skillet over medium heat.
Read the full answer

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-5.6 Luna Pro2,250 words
I would treat this as an urgent patient-safety and governance event, not as an earnings-management problem. A suspected fatal or life-threatening adverse effect affecting potentially hundreds of patients is sufficient to trigger immediate escalation, investigation, and regulator contact.
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GPT-6 Sol986 words
I would not wait six months or wait for the earnings call. An internal signal of liver failure in a widely used drug warrants immediate patient-protection measures and prompt contact with regulators, even while causality and the precise risk are being checked.
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-5.6 Luna Pro2,940 words
This agreement is heavily one-sided and leaves several material issues undefined. Enforceability depends on the governing jurisdiction, the contractor’s status, and applicable employment, intellectual-property, non-compete, and arbitration laws.
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GPT-6 Sol1,032 words
This draft is heavily one-sided. Every numbered section contains a term the Client could use against the Contractor. The suggestions below are negotiating language, not a determination that a clause is enforceable: that depends on the governing law, the parties’ locations, and the facts of the engagement.
Read the full answer

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 Luna Pro826 words
For an experienced software engineer A language model is trained on large collections of text by repeatedly hiding or withholding the next token and asking the model to predict it. “Token” usually means a word fragment rather than a complete word.
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GPT-6 Sol617 words
Experienced software engineer Think of a language model as a service whose API accepts a sequence of tokens and returns a probability distribution over the next token. During training, it sees enormous numbers of text sequences and adjusts billions of parameters to make the tokens that actually followed more likely.
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Advanced Longevity Plan (Biohacker)

Develop a comprehensive, cutting-edge 3-month longevity plan for a biohacker aiming to optimize longevity, physical and cognitive…

GPT-5.6 Luna Pro2,606 words
12-Week Longevity and Performance Plan This plan is designed for a generally healthy adult seeking better cardiometabolic health, physical capacity, cognitive performance, and recovery. It is not a substitute for medical care.
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GPT-6 Sol1,402 words
A 12-week longevity and performance plan The highest-confidence longevity strategy is not a large supplement stack. It is consistent sleep, resistance training, aerobic fitness, adequate nutrition, cardiometabolic risk management, and avoiding tobacco.
Read the full answer
Our Verdict
GPT-6 Sol
GPT-6 Sol
GPT-5.6 Luna Pro
GPT-5.6 Luna ProRunner-up

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

Too close to call

Reviewing agent-written code?See a Brief PR report

API pricing

Cost per 1M tokens

GPT-5.6 Luna Pro
Input
$1.00
2.0× cheaper
Output
$6.00
1.7× cheaper
GPT-6 Sol
Input
$2.00
Output
$10.00

GPT-5.6 Luna Pro is cheaper on both: 2.0× input, 1.7× output.

Where to run it

5 hosts, cheapest first

GPT-5.6 Luna Pro2 hosts
HostInOutContextUptime
Azure AI Foundry$0.20 in·$1.20 out·1.1M·98.2% upOpenAI$0.20 in·$1.20 out·1.1M·99.9% up
GPT-6 Sol3 hosts
HostInOutContextUptime
Azure AI Foundry$2.00 in·$10.00 out·1.1M·96.6% upOpenAI$2.00 in·$10.00 out·1.1M·100% upAmazon Bedrock$2.20 in·$11.00 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 Pro has a 1.1M token context window vs GPT-6 Sol'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 Pro and GPT-6 Sol 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 Pro costs $1/M input tokens and GPT-6 Sol costs $2/M input tokens. GPT-5.6 Luna Pro is $1.00/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 Pro and GPT-6 Sol 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

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GPT-5.6 Luna Pro58 outputs, specs and price
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