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  5. GPT-5.4vsGPT-6 Luna
Updated Sep 2026

GPT-5.4vsGPT-6 Luna

GPT-6 Luna is cheaper than GPT-5.4 at $0.1/M vs $2.5/M input tokens.

GPT-5.4 and GPT-6 Luna compared across 20 shared prompts
SpecGPT-5.4GPT-6 Luna
Input price$2.5/M tokens$0.1/M tokens
Output price$15/M tokens$0.5/M tokens
Context window1.1M tokens1.1M tokens
WeightsClosedClosed
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-5.42,522 words
Here are the main contractor-unfriendly clauses, why they’re risky, and concrete redlines you should consider. This is business/legal information, not legal advice; for an actual engagement, a lawyer in the relevant jurisdiction should review it.
Read the full answer
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

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-5.4169 words
Creative Name: Golden Crunch Honey Garlic Noodles 7 Pantry Ingredients: Spaghetti or any noodles Garlic Soy sauce Honey Olive oil Red pepper flakes Breadcrumbs Estimated Time: Prep: 5 minutes Cook: 12 minutes Total: 17 minutes Instructions: 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-5.42,705 words
I would act as if this will become public soon, because ethically and practically that is the safest assumption. The core principle: patient safety first, evidence preserved, regulators informed promptly, and no misleading statements to investors or physicians.
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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

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-5.41,307 words
LedgerLift (LLLT) — Internal IC Memo Recommendation: Long Current Price: $46 12-month PT range: $58–$74 (base-centered fair value ~$66; downside ~$47; upside ~$86 on DCF, but we cap 12-month bull PT at $74 to reflect execution/rating risk) Two-sentence thesis: LedgerLift screens as a high-quality vertical SaaS/fintech…
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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.
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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-5.41,258 words
Below is a simplified 5-year LBO model for HarborTech Services (HTS) using only the assumptions provided. Entry, sources & uses Purchase price FY2025 EBITDA = $120.0m Entry multiple = 12.0x Enterprise Value = 12.0 × 120.0 = $1,440.0m Fees Transaction fees = 2.0% of EV = 2.0% × 1,440.0 = $28.8m Uses Purchase of…
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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.
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Debug This Architecture

Here's the architecture for a real-time collaborative document editor (like Google Docs): **System Overview:** - Frontend: React SPA with…

GPT-5.42,980 words
Here’s a structured teardown of the architecture: failure modes, race conditions, correctness issues, security problems, and scaling bottlenecks — plus concrete fixes and trade-offs.
Read the full answer
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.
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Our Verdict
GPT-5.4
GPT-5.4
GPT-6 Luna
GPT-6 Luna

Not enough votes to call it. On the specs, nothing separates them.

GPT-6 Luna costs 30x less per token.

Too close to call

Reviewing agent-written code?See a Brief PR report

API pricing

Cost per 1M tokens

GPT-5.4
Input
$2.50
Output
$15.00
GPT-6 Luna
Input
$0.10
25× cheaper
Output
$0.50
30× cheaper

GPT-6 Luna is cheaper on both: 25× input, 30× output.

Where to run it

6 hosts, cheapest first

GPT-5.43 hosts
HostInOutContextUptime
Azure AI Foundry$2.50 in·$15.00 out·1.1M·100% upOpenAI$2.50 in·$15.00 out·1.1M·99.9% upAmazon Bedrock$2.75 in·$16.50 out·1.1M—
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-5.4 has a 1.1M 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-5.4 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-5.4 costs $2.5/M input tokens and GPT-6 Luna costs $0.1/M input tokens. GPT-6 Luna is $2.40/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-5.4 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-5.4 logo
GPT-5.453 outputs, specs and price
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GPT-6 Luna20 outputs, specs and price
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