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  5. GPT-5.3 ChatvsGPT-6 Luna Pro
Updated Sep 2026

GPT-5.3 ChatvsGPT-6 Luna Pro

GPT-6 Luna Pro is cheaper than GPT-5.3 Chat at $0.1/M vs $1.75/M input tokens.

GPT-5.3 Chat and GPT-6 Luna Pro compared across 20 shared prompts
SpecGPT-5.3 ChatGPT-6 Luna Pro
Input price$1.75/M tokens$0.1/M tokens
Output price$14/M tokens$0.5/M tokens
Context window128K tokens1.1M tokens
Weights—Closed
Free API (OpenRouter)NoNo
ReleasedMar 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-5.3 Chat135 words
Dish name: Golden Honey Garlic Noodles Ingredients (7): Spaghetti or any dried noodles Garlic Honey Soy sauce Butter Red pepper flakes Black pepper Estimated time: 15 minutes Instructions: Bring a pot of salted water to a boil and cook the noodles according to package directions.
Read the full answer
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…
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-5.3 Chat782 words
Key issues fall into consistency, real‑time propagation, storage, scaling, and security. WebSocket broadcast only reaches clients on the same server Problem: Each server only broadcasts to its own connections. Clients connected to other servers only see updates after the 2‑second polling delay.
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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

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-5.3 Chat785 words
Dish name: “Forest & Tide: Scallop, Aged Soy, Pine, and Dark Chocolate” Concept narrative This dish explores the meeting point of ocean depth and forest aromatics. Sweet raw scallop is paired with an unexpected partner: extremely light dark chocolate bitterness and pine brightness.
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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.
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-5.3 Chat361 words
Goal: build a few simple habits you can sustain. Focus areas: diet, movement, sleep. Keep it easy and consistent. Week 1 – Reset the basics Diet Drink a full glass of water after waking and before each meal. Add one fruit or vegetable to every meal. Reduce sugary drinks; replace with water or unsweetened tea.
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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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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-5.3 Chat1,103 words
Investment Committee Memo – LedgerLift (LLLT) Recommendation: LONG Current Price: $46 12‑month PT range: $60–$78 (base‑weighted fair value ~$68) Thesis (2 sentences): LedgerLift is a high‑quality vertical SaaS platform in B2B spend management with strong retention (123% NRR), attractive unit economics (18‑month CAC…
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GPT-6 Luna Pro888 words
LedgerLift (LLLT) — Investment Committee Memo Recommendation: Pass 12-month price target range: $28–44 per share LedgerLift has attractive customer economics, recurring revenue, and a credible path to margin expansion, but those strengths are already reflected in a $46 share price.
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Mini LBO Underwrite

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

GPT-5.3 Chat844 words
All figures in $ millions unless noted. ENTRY (end FY2025) EBITDA = 120 Enterprise value = 12.0 × 120 = 1,440 Transaction fees = 2% × 1,440 = 28.8 Debt at close Term Loan = 4.0 × 120 = 480 Mezzanine = 1.5 × 120 = 180 Equity = EV − Debt + fees = 1,440 − 660 + 28.8 = 808.8 Starting balances Term Loan = 480 Mezz = 180…
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GPT-6 Luna Pro434 words
Operating and debt schedule Conventions: Interest is calculated on beginning-of-year debt; the 1% Term Loan amortization is 1% of its original $480m principal ($4.8m annually). Mezzanine PIK accrues at 2% annually.
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Our Verdict
GPT-6 Luna Pro
GPT-6 Luna Pro
GPT-5.3 Chat
GPT-5.3 ChatRunner-up

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

GPT-6 Luna Pro costs 28x less per token.

Too close to call

Reviewing agent-written code?See a Brief PR report

API pricing

Cost per 1M tokens

GPT-5.3 Chat
Input
$1.75
Output
$14.00
GPT-6 Luna Pro
Input
$0.10
18× cheaper
Output
$0.50
28× cheaper

GPT-6 Luna Pro is cheaper on both: 18× input, 28× output.

Where to run it

2 hosts

GPT-5.3 Chat

No hosts listed on OpenRouter.

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-5.3 Chat has a 128K 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-5.3 Chat 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-5.3 Chat costs $1.75/M input tokens and GPT-6 Luna Pro costs $0.1/M input tokens. GPT-6 Luna Pro is $1.65/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-5.3 Chat 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-5.3 Chat logo
GPT-5.3 Chat53 outputs, specs and price
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