Skip to content
Rival
How it worksPrivacyTerms
Explore all of Rival

Explore

  • Compare Models
  • All Models
  • Image Comparison
  • Audio Comparison
  • Image Generation
  • Best AI For...
  • Arena
  • API Pricing
  • Challenges

Discover

  • SubjectiveBench
  • Default Index
  • Research
  • Research downloads
  • Rival Kits
  • Find your AI taste
  • UI Glow-Up
  • VoiceLock
  • Cost Cutter
  • Agent skills
  • Benchmarks vs Vibes
  • Brief
  • Jailbreak
  • Model Updates
  • Provider Status
  • AI Creators

Connect

  • Methodology
  • Advertise
  • Partnerships
  • Privacy Policy
  • Terms
  • RSS Feed
  1. Home
  2. /
  3. Compare
  4. /
  5. GPT-5.1 ChatvsGPT-6 Luna
Updated Sep 2026

GPT-5.1 ChatvsGPT-6 Luna

GPT-6 Luna is cheaper than GPT-5.1 Chat at $0.1/M vs $1.25/M input tokens.

GPT-5.1 Chat and GPT-6 Luna compared across 20 shared prompts
SpecGPT-5.1 ChatGPT-6 Luna
Input price$1.25/M tokens$0.1/M tokens
Output price$10/M tokens$0.5/M tokens
Context window128K tokens1.1M tokens
Weights—Closed
Free API (OpenRouter)NoNo
ReleasedNov 2025Sep 2026
Side by side

Same prompt, both answers

Opening lines from 4 of the 20 prompts both answered. Formatting stripped, words untouched.

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-5.1 Chat905 words
1) Recommendation, PT Range, Two‑Sentence Thesis Recommendation: Long 12‑month PT range: $63–$78 Thesis (2 sentences): LedgerLift is a mid‑market spend‑management platform with best‑in‑class retention, strong NRR, and a durable subscription mix that supports compounding cash generation as operating leverage…
Read the full answer
GPT-6 Luna896 words
LedgerLift (LLLT) — Investment Committee Memo Recommendation: Short 12-month price target: $28–$42 At $46, LedgerLift’s price implies continued strong growth and margin expansion; our DCF scenarios value the shares at approximately $17–$42, with the base case near $28.
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-5.1 Chat191 words
Here’s a simple, beginner‑friendly 1‑month plan focused on diet, exercise, and sleep. Diet • Week 1: Add one serving of vegetables to one meal each day. • Week 2: Swap one processed snack (chips, cookies) for fruit, nuts, or yogurt. • Week 3: Aim for one balanced plate per day (protein, vegetables, healthy carbs).
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-5.1 Chat111 words
Sweet Citrus Cloud Squares Ingredients (7 total) 1 cup all-purpose flour 1 cup sugar 1 cup plain yogurt 2 eggs 1 teaspoon baking powder Zest of 1 lemon 2 tablespoons melted butter Instructions Preheat oven to 350°F (175°C). Lightly grease an 8x8 baking dish.
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

Mini LBO Underwrite

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

GPT-5.1 Chat391 words
Below is a clean, concise underwriting output following your instructions. YEAR‑BY‑YEAR SUMMARY (FY26–FY30) All figures in $m. Term loan = 480 initial; mezzanine = 180 initial. Optional amortization applied.
Read the full answer
GPT-6 Luna405 words
All figures in $m. Assumptions: annual Term Loan amortization is 1% of original principal ($4.8m); cash interest is based on beginning-of-year balances; Mezz PIK compounds annually.
Read the full answer
Our Verdict
GPT-6 Luna
GPT-6 Luna
GPT-5.1 Chat
GPT-5.1 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 20x less per token.

Too close to call

Reviewing agent-written code?See a Brief PR report

API pricing

Cost per 1M tokens

GPT-5.1 Chat
Input
$1.25
Output
$10.00
GPT-6 Luna
Input
$0.10
13× cheaper
Output
$0.50
20× cheaper

GPT-6 Luna is cheaper on both: 13× input, 20× output.

Where to run it

3 hosts, cheapest first

GPT-5.1 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-5.1 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-5.1 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-5.1 Chat costs $1.25/M input tokens and GPT-6 Luna costs $0.1/M input tokens. GPT-6 Luna is $1.15/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-5.1 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.

Keep exploring

More comparisons

Against the newest arrivals

GPT-5.1 Chat logoSolar Mini 4 logo
GPT-5.1 Chat vs Solar Mini 4Landed Sep 2026
GPT-6 Luna logoQwen3.8 Max Prime logo
GPT-6 Luna vs Qwen3.8 Max PrimeLanded Sep 2026
GPT-5.1 Chat logoGLM 5.3 Prime logo
GPT-5.1 Chat vs GLM 5.3 PrimeLanded Sep 2026
GPT-6 Luna logoQwen3.8 Omni Flash logo
GPT-6 Luna vs Qwen3.8 Omni FlashLanded Sep 2026
GPT-5.1 Chat logoCommand A+ logo
GPT-5.1 Chat vs Command A+Landed Sep 2026
GPT-6 Luna logoClaude Opus 5.5 logo
GPT-6 Luna vs Claude Opus 5.5Landed Sep 2026
GPT-5.1 Chat logoGPT-6 Luna Pro logo
GPT-5.1 Chat vs GPT-6 Luna ProLanded Sep 2026
GPT-6 Luna logoGPT-6 Sol Pro logo
GPT-6 Luna vs GPT-6 Sol ProLanded Sep 2026

Same lab, same size, long tail

GPT-5.1 Chat logoGPT-6 Sol Pro logo
GPT-5.1 Chat vs GPT-6 Sol ProSame lab
GPT-5.1 Chat logoGPT-6 Sol logo
GPT-5.1 Chat vs GPT-6 SolSame lab
GPT-6 Luna logoGPT-6 Luna Pro logo
GPT-6 Luna vs GPT-6 Luna ProSame lab
GPT-6 Luna logoGPT-6 Sol logo
GPT-6 Luna vs GPT-6 SolSame lab
GPT-6 Luna logoGLM 4.7 logo
GPT-6 Luna vs GLM 4.7Same size
GPT-6 Luna logoGLM 4.7 Flash logo
GPT-6 Luna vs GLM 4.7 FlashNew provider
GPT-5.1 Chat logoGLM 5 logo
GPT-5.1 Chat vs GLM 5New provider
GPT-5.1 Chat logoGLM 5 Turbo logo
GPT-5.1 Chat vs GLM 5 TurboNew provider

Model pages

GPT-5.1 Chat logo
GPT-5.1 Chat53 outputs, specs and price
GPT-6 Luna logo
GPT-6 Luna20 outputs, specs and price
Rival
How it worksPrivacyTerms
Explore all of Rival

Explore

  • Compare Models
  • All Models
  • Image Comparison
  • Audio Comparison
  • Image Generation
  • Best AI For...
  • Arena
  • API Pricing
  • Challenges

Discover

  • SubjectiveBench
  • Default Index
  • Research
  • Research downloads
  • Rival Kits
  • Find your AI taste
  • UI Glow-Up
  • VoiceLock
  • Cost Cutter
  • Agent skills
  • Benchmarks vs Vibes
  • Brief
  • Jailbreak
  • Model Updates
  • Provider Status
  • AI Creators

Connect

  • Methodology
  • Advertise
  • Partnerships
  • Privacy Policy
  • Terms
  • RSS Feed