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

GPT-5.6 LunavsGPT-6 Sol Pro

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

GPT-5.6 Luna and GPT-6 Sol Pro compared across 20 shared prompts
SpecGPT-5.6 LunaGPT-6 Sol Pro
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.

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 Luna2,537 words
12-Week Longevity and Performance Plan This is a structured framework for a generally healthy adult, not a substitute for medical care. Before starting, obtain clinician clearance if you have cardiovascular disease, diabetes, kidney/liver disease, a history of eating disorders, sleep apnea, are pregnant, take…
Read the full answer
GPT-6 Sol Pro1,411 words
A 12-week longevity and performance plan Aim: improve the health markers most strongly linked to long-term outcomes—cardiorespiratory fitness, strength, blood pressure, metabolic health, sleep, and sustainable habits—while testing whether more experimental “biohacks” add anything useful.
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-5.6 Luna1,093 words
LedgerLift (LLLT) — Internal Investment Committee Memo Recommendation Recommendation: Pass 12-month fair-value range: $35–$50 per share versus $46 currently. Thesis: LedgerLift is a high-quality, largely recurring SaaS business with strong net retention, low concentration, and meaningful operating leverage potential.
Read the full answer
GPT-6 Sol Pro974 words
LedgerLift (LLLT) — Investment Committee Memo Recommendation: Short 12-month price target: $30–$44 Thesis. LedgerLift has attractive subscription economics, but at $46 the stock prices in substantially more durable cash flow than the supplied operating assumptions produce: base-case DCF value is about $28 per share…
Read the full answer

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.
Read the full answer
GPT-6 Sol Pro1,277 words
The central problem is that this design treats concurrent edits as independent database writes, then tries to reconcile them with client timestamps. That can lose valid edits even when every component is working.
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 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 Sol Pro970 words
This is a strongly one-sided draft. Do not sign it as written. The enforceability of particular terms—especially the non-compete, payment provisions, and arbitration clause—depends on the governing jurisdiction, which the agreement does not identify.
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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 Sol Pro114 words
Golden Pantry Chickpea Patties Prep: 10 minutes · Cook: 8 minutes · Makes: 6 small patties Ingredients — just 7 1 can (15 oz) chickpeas, drained 3 tbsp all-purpose flour 2 tbsp water 2 tbsp olive oil 1 tsp garlic powder 1 tsp paprika ½ tsp salt Instructions Mash the chickpeas with a fork, leaving a few chunky bits.
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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 Sol Pro913 words
Scallop, Green Strawberry & White Chocolate Seared scallops with charred kohlrabi, compressed green strawberry, white-chocolate–miso beurre blanc, kombu oil and buckwheat lace The unusual pairing is scallop and white chocolate.
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Our Verdict
GPT-6 Sol Pro
GPT-6 Sol Pro
GPT-5.6 Luna
GPT-5.6 LunaRunner-up

Not enough votes to call it. On the specs, GPT-6 Sol Pro 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
Input
$1.00
2.0× cheaper
Output
$6.00
1.7× cheaper
GPT-6 Sol Pro
Input
$2.00
Output
$10.00

GPT-5.6 Luna is cheaper on both: 2.0× input, 1.7× 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 Sol Pro2 hosts
HostInOutContextUptime
Azure AI Foundry$2.00 in·$10.00 out·1.1M·99.9% upOpenAI$2.00 in·$10.00 out·1.1M·100% 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 Sol 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 Sol 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 Sol Pro costs $2/M input tokens. GPT-5.6 Luna 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 and GPT-6 Sol 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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Same lab, same size, long tail

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Model pages

GPT-5.6 Luna logo
GPT-5.6 Luna58 outputs, specs and price
GPT-6 Sol Pro logo
GPT-6 Sol Pro20 outputs, specs and price
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