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

GPT-5.3 ChatvsGPT-6 Luna

GPT-6 Luna 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 compared across 20 shared prompts
SpecGPT-5.3 ChatGPT-6 Luna
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.

Adversarial Contract Review

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

GPT-5.3 Chat802 words
Several clauses are unusually one‑sided and could expose the contractor to major financial or professional risk. Below are the main issues, suggested changes, and why they matter. Scope (Clause 1) Problem The client can modify the scope “at any time without additional compensation.”
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GPT-6 Luna2,040 words
This agreement is strongly one-sided. The enforceability of particular terms—especially the non-compete, liability provisions, and arbitration clause—depends on the governing law and the facts. The agreement does not identify a governing law, which is itself a significant gap.
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.
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

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 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

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-5.3 Chat718 words
0–2 hours • Verify the signal immediately. Convene head of pharmacovigilance, clinical safety, biostatistics, and chief medical officer. Require raw data, case narratives, statistical analysis, and comparison to baseline liver‑failure incidence.
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GPT-6 Luna1,930 words
I would not wait six months for more data. A potentially fatal signal affecting a drug used by millions requires immediate safety assessment, prompt engagement with regulators, and a plan to inform patients and clinicians.
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.
Read the full answer
GPT-6 Luna1,249 words
Turbot, White Asparagus, Green Strawberry Kosho & Toasted-Hay Beurre Blanc A composed spring dish for four, built around an unusual pairing: tart green strawberry and toasted hay.
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 Luna1,979 words
The main architectural risk is that the system treats collaborative editing as “write a value, then broadcast it.” That works poorly under concurrency, server failures, reconnects, and scale.
Read the full answer
Our Verdict
GPT-6 Luna
GPT-6 Luna
GPT-5.3 Chat
GPT-5.3 ChatRunner-up

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

GPT-6 Luna 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
Input
$0.10
18× cheaper
Output
$0.50
28× cheaper

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

Where to run it

3 hosts, cheapest first

GPT-5.3 Chat

No hosts listed on OpenRouter.

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-5.3 Chat has a 128K 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-5.3 Chat 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-5.3 Chat costs $1.75/M input tokens and GPT-6 Luna costs $0.1/M input tokens. GPT-6 Luna 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 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
GPT-6 Luna logo
GPT-6 Luna20 outputs, specs and price
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