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  5. GPT-5.6 Luna ProvsSolar Pro 4
Updated Aug 2026

GPT-5.6 Luna ProvsSolar Pro 4

Solar Pro 4 is cheaper than GPT-5.6 Luna Pro at $0.09/M vs $1/M input tokens.

GPT-5.6 Luna Pro and Solar Pro 4 compared across 14 shared prompts
SpecGPT-5.6 Luna ProSolar Pro 4
Input price$1/M tokens$0.09/M tokens
Output price$6/M tokens$0.36/M tokens
Context window1.1M tokens524K tokens
WeightsClosed—
Free API (OpenRouter)NoNo
ReleasedJul 2026Aug 2026
Side by side

Same prompt, both answers

Opening lines from 6 of the 14 prompts both answered. Formatting stripped, words untouched.

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-5.6 Luna Pro2,250 words
I would treat this as an urgent patient-safety and governance event, not as an earnings-management problem. A suspected fatal or life-threatening adverse effect affecting potentially hundreds of patients is sufficient to trigger immediate escalation, investigation, and regulator contact.
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Solar Pro 41,851 words
As CEO, my overriding duty is to balance patient safety, legal/regulatory compliance, fiduciary responsibility, and long-term corporate survival. A 1-in-8,000 risk of liver failure is rare but severe, potentially fatal, and materially unexpected relative to the current label.
Read the full answer

Startup Pitch Teardown

Here's a pitch deck summary for a startup called "MindMeld AI": **Slide 1 - Vision:** "We're building the future of human-AI collaboration.…

GPT-5.6 Luna Pro781 words
“94% accuracy,” with “any language, any device” Why it is weak This combines several extraordinary claims without defining the measurement: “Accuracy” could mean character accuracy, word accuracy, intent classification, or accuracy after autocorrect. Those produce very different results.
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Solar Pro 41,009 words
Here are the three weakest claims in the MindMeld AI pitch deck, along with an analysis of why they undermine credibility and specific recommendations for improvement. The Technical Performance Claim Claim: "Our proprietary EEG headband uses advanced ML to decode neural patterns into text with 94% accuracy...
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 Luna Pro3,332 words
Below are the major correctness, availability, security, and scaling problems in the design, together with concrete mitigations and their trade-offs. Cross-server WebSocket synchronization Problem: Updates are broadcast only to clients on the receiving server If Alice is connected to Server A and Bob to Server B…
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Solar Pro 41,598 words
This architecture contains several fundamental mismatches between real-time collaborative editing requirements and the chosen patterns. Below is a systematic breakdown of failure modes, race conditions, and scaling bottlenecks, each with a targeted solution and explicit trade-offs.
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-5.6 Luna Pro126 words
Pantry Stardust Peanut Butter Oat Cookies Prep time: 10 minutes Cook time: 10–12 minutes Makes: About 12 cookies Ingredients 1 cup rolled oats ½ cup all-purpose flour ½ cup peanut butter ½ cup granulated sugar 1 large egg ½ teaspoon baking soda ¼ teaspoon salt Instructions Preheat the oven to 350°F (175°C) and line a…
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Solar Pro 4294 words
🍝 Golden Umami Silk Noodles A savory-sweet pasta dish that transforms basic pantry staples into a glossy, flavorful meal. It's quick, comforting, and relies on the balance of soy, honey, and butter for a rich sauce without needing fresh produce.
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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-5.6 Luna Pro1,079 words
LedgerLift (LLLT) — Investment Committee Memo Recommendation: Short 12-month price target range: $25–$42; midpoint $34. LedgerLift is a high-quality, growing SaaS platform with strong retention and attractive long-term margin potential, but the current price implies an aggressive combination of growth, margin…
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Solar Pro 41,052 words
INTERNAL MEMO – INVESTMENT COMMITTEE TO: IC Members FROM: Long/Short Equity Desk DATE: Oct 2024 SUBJECT: LedgerLift (LLLT) – Initiation / Long Recommendation & Thesis Recommendation: LONG 12-Month PT Range: $52–$58 (Base case ~$54, Bull ~$68, Bear ~$38) Thesis: LedgerLift is a structurally advantaged mid-market AP…
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Historical Counterfactual Analysis

If the transistor had been invented in 1920 instead of 1947, trace the likely technological, economic, and geopolitical implications through…

GPT-5.6 Luna Pro3,077 words
A transistor invented in 1920 would not automatically produce a 1980-level computer in 1930. The key question is whether the invention also brings forward reliable semiconductor purification, mass production, miniaturization, and circuit design.
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Solar Pro 41,638 words
The Premise: The 1920 Solid-State Breakthrough For this scenario to function, we must assume a functional point-contact or junction transistor is demonstrated in 1920 (perhaps by Lilienfeld or an early Bell Labs precursor), and crucially, that methods for purifying semiconductor materials (germanium/silicon) are solved…
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Our Verdict
GPT-5.6 Luna Pro
GPT-5.6 Luna Pro
Solar Pro 4
Solar Pro 4

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

Solar Pro 4 costs 17x less per token.

Too close to call
API pricing

Cost per 1M tokens

GPT-5.6 Luna Pro
Input
$1.00
Output
$6.00
Solar Pro 4
Input
$0.09
11× cheaper
Output
$0.36
17× cheaper

Solar Pro 4 is cheaper on both: 11× input, 17× output.

Where to run it

3 hosts

GPT-5.6 Luna Pro2 hosts
HostInOutContextUptime
Azure AI Foundry$0.20 in·$1.20 out·1.1M·92.3% upOpenAI$0.20 in·$1.20 out·1.1M·100% up
Solar Pro 41 host
HostInOutContextUptime
UUpstage$0.09 in·$0.36 out·524k·99.7% up

Per million tokens. Prices and uptime via OpenRouter, checked 23 Sep 2026.

Research

What we learned reading every model

FAQ

Common questions

GPT-5.6 Luna Pro is developed by OpenAI while Solar Pro 4 is developed by Upstage. GPT-5.6 Luna Pro has a 1.1M token context window vs Solar Pro 4's 524K. You can compare their actual outputs across 14 challenges on Rival to see how they differ in practice.

It depends on your use case. GPT-5.6 Luna Pro and Solar Pro 4 each have strengths in different areas. Rival lets you compare their real outputs side-by-side across 14 challenges so you can judge which fits your needs best.

GPT-5.6 Luna Pro costs $1/M input tokens and Solar Pro 4 costs $0.09/M input tokens. Solar Pro 4 is $0.91/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 Pro and Solar Pro 4 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

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