GPT-6 Luna · Writing
GPT-6 Luna for writing: our test runs
GPT-6 Luna ran our 5 writing prompts in llmwise, through the same pipeline your messages take. Here's every reply as it came, whether it passed, what it cost and what it counts as on Pro, next to the other models.
Based on 5 of our test runs on , through OpenRouter with the app's own prompt and settings. Updated .
Short answer
In our test runs on September 27, 2026, GPT-6 Luna passed 5 of 5 of our writing prompts (both hard ones): tied 1st of 20 models. Each reply counted as 1 message on Pro, where it has 60 a day, and cost $0.0001 to run on average.
Prompt by prompt
Each of the 5 writing prompts, and how GPT-6 Luna's reply did.
| Prompt | Result | Cost | Time |
|---|---|---|---|
| Announce a second bakery shop on LinkedInEveryday | Passed: Graded 4.5 of 5 on average (lowest 4). | $0.0001 | 2.9 s |
| Rewrite corporate jargon in plain wordsEveryday | Passed: Graded 4.7 of 5 on average (lowest 4). | $0.0001 | 2.4 s |
| Decline a meeting and offer two timesEveryday | Passed: Graded 5.0 of 5 on average (lowest 5). | $0.0001 | 1.3 s |
| A product announcement with five rulesHard | Passed: Graded 4.0 of 5 on average (lowest 3). | $0.0001 | 1.5 s |
| Argue both sides of free busesHard | Passed: Graded 4.3 of 5 on average (lowest 4). | $0.0001 | 2.5 s |
Every writing reply from GPT-6 Luna
Announce a second bakery shop on LinkedIn
An everyday prompt: “Announce a second bakery shop on LinkedIn”, in full.
Passed: Graded 4.5 of 5 on average (lowest 4).
We’re delighted to share that Crumb & Co. is opening a second shop in Leeds on 14 November! What began as one small bakery has grown thanks to the lovely people who’ve stopped by, shared a loaf, and made us feel part of the community. We’re excited to bring our freshly baked bread, pastries, and warm welcomes to a new neighbourhood. To celebrate opening day, we’ll be giving away free coffee. Pop in, say hello, and enjoy a cup with us—we’d love to meet you. Thank you to everyone who has supported Crumb & Co. so far. We can’t wait to open the doors and start this next chapter together. See you in Leeds on 14 November!
389 tokens in, 149 out · 2.9 s · $0.0001 · 1 message on Pro · answered by openai/gpt-6-luna via OpenAI ·
Rewrite corporate jargon in plain words
An everyday prompt: “Rewrite corporate jargon in plain words”, in full.
Passed: Graded 4.7 of 5 on average (lowest 4).
In Q3, teams across the company worked together to focus more on customers. Retention measures improved by 12%, and the rate of customer loss fell by 0.3 percentage points in the enterprise segment. The company also adjusted its customer contact channels to make better use of available capacity.
417 tokens in, 124 out (59 of them reasoning) · 2.4 s · $0.0001 · 1 message on Pro · answered by openai/gpt-6-luna via OpenAI ·
Decline a meeting and offer two times
An everyday prompt: “Decline a meeting and offer two times”, in full.
Passed: Graded 5.0 of 5 on average (lowest 5).
Subject: Vendor Demo Hi Tom, Thanks for the invitation. I’m presenting to the board on Wednesday at 11:00, so I can’t make the demo then. Would Thursday at 10:00 or Friday at 14:00 work instead? Best, [Your Name]
395 tokens in, 64 out · 1.3 s · $0.0001 · 1 message on Pro · answered by openai/gpt-6-luna via OpenAI ·
A product announcement with five rules
A hard prompt: “A product announcement with five rules”, in full.
Passed: Graded 4.0 of 5 on average (lowest 3).
Meet the Nordvik 2, a desk lamp designed to bring flexible light to your workspace. Choose from five brightness levels, charge it via USB-C, and turn its arm up to 270 degrees to direct light where you need it. The Nordvik 2 costs €79 and ships on 1 December. Ready to brighten your desk?
406 tokens in, 73 out · 1.5 s · $0.0001 · 1 message on Pro · answered by openai/gpt-6-luna via OpenAI ·
Argue both sides of free buses
A hard prompt: “Argue both sides of free buses”, in full.
Passed: Graded 4.3 of 5 on average (lowest 4).
Making buses free would give every resident reliable access to jobs, school, health care, and daily necessities, regardless of income. It would also speed boarding, reduce fare-enforcement costs, and encourage people to leave cars at home—easing congestion, pollution, and parking pressure. A city that treats public transit as essential infrastructure, rather than a service people must qualify to afford, can build a more connected and equitable community. But “free” buses still have to be paid for, and the bill could divert money from more urgent improvements: frequent service, safer stops, cleaner vehicles, and routes to underserved neighborhoods. If buses remain slow, crowded, or unreliable, removing fares may do little to persuade drivers to switch, while reducing funds that could make transit genuinely useful. Targeted fare assistance can protect riders who need it most without subsidizing every trip, including those by people who can readily afford to pay.
384 tokens in, 186 out · 2.5 s · $0.0001 · 1 message on Pro · answered by openai/gpt-6-luna via OpenAI ·
How it compares on writing
GPT-6 Luna beside the job's picks among every model. 3 models share the hard-problems pick, GPT-6 Luna among them.
| Model | Passed | On Pro | Cost per reply |
|---|---|---|---|
| DeepSeek V4 ProOur pick: hard problems (shared), best value | 5 of 5 | 250 a month on Pro | $0.0011 |
| GPT-6 LunaOur pick: hard problems (shared), everyday | 5 of 5 | 60 a day on Pro | $0.0001 |
Every limit is published. Paid plans also have a monthly fair-use limit on AI cost: Plus $3.75, Pro $7.50, Max $20, Ultra $42, Studio $85. Using every message on your plan at typical sizes stays under it; very large messages and heavy research use it faster. Every limit, explained.
GPT-6 Luna next to each model on writing
GPT-6 Luna against each model on the same 5 writing prompts. One run each, through OpenRouter: a wait depends on the provider and the load that day, so a lead under 10% counts as close.
Against Claude Fable 5.1: GPT-6 Luna answered 2.5× sooner (2.4 s to 6.0 s), cost 173.5× less, and passed 5 of 5 to its 3. Only GPT-6 Luna passed A product announcement with five rules; Argue both sides of free buses.
Against Claude Opus 5.5: GPT-6 Luna answered 3.5× sooner (2.4 s to 8.2 s), cost 185.7× less, and passed 5 of 5 to its 4. Only GPT-6 Luna passed Argue both sides of free buses.
Against Claude Sonnet 5.5: GPT-6 Luna answered within 10% of its time (2.4 s to 2.3 s), cost 34.3× less, and passed 5 of 5 to its 4. Only GPT-6 Luna passed Argue both sides of free buses.
Against Claude Sonnet 5: GPT-6 Luna answered 1.9× sooner (2.4 s to 4.5 s), cost 34.3× less, and passed 5 of 5 to its 4. Only GPT-6 Luna passed Announce a second bakery shop on LinkedIn.
Against Claude Haiku 5.5: GPT-6 Luna answered 1.6× later (2.4 s to 1.5 s), cost 1.6× less, and passed 5 of 5 to its 3. Only GPT-6 Luna passed Rewrite corporate jargon in plain words; Argue both sides of free buses.
Against Claude Haiku 4.5: GPT-6 Luna answered within 10% of its time (2.4 s to 2.2 s), cost 11.4× less, and passed 5 of 5 to its 4. Only GPT-6 Luna passed A product announcement with five rules.
Against GPT-6 Astra: GPT-6 Luna answered 2.0× sooner (2.4 s to 4.8 s), cost 111.8× less, and passed 5 of 5 to its 5.
Against GPT-6.1 Sol: GPT-6 Luna answered 1.4× sooner (2.4 s to 3.3 s), cost 11.4× less, and passed 5 of 5 to its 4. Only GPT-6 Luna passed Rewrite corporate jargon in plain words.
Against GPT-6 Sol: GPT-6 Luna answered 1.4× sooner (2.4 s to 3.5 s), cost 22.8× less, and passed 5 of 5 to its 4. Only GPT-6 Luna passed Rewrite corporate jargon in plain words.
Against Gemini 4 Argon: GPT-6 Luna answered 2.4× sooner (2.4 s to 5.7 s), cost 14.1× less, and passed 5 of 5 to its 4. Only GPT-6 Luna passed Argue both sides of free buses.
Against Gemini 3.1 Pro (preview): GPT-6 Luna answered 3.8× sooner (2.4 s to 9.1 s), cost 92.3× less, and passed 5 of 5 to its 4. Only GPT-6 Luna passed Argue both sides of free buses.
Against Gemini 3.8 Flash: GPT-6 Luna answered 1.6× sooner (2.4 s to 3.9 s), cost 13.3× less, and passed 5 of 5 to its 3. Only GPT-6 Luna passed Rewrite corporate jargon in plain words; A product announcement with five rules.
Against DeepSeek V4.1 Flash: GPT-6 Luna answered 1.8× later (2.4 s to 1.3 s), cost 4.5× less, and passed 5 of 5 to its 4. Only GPT-6 Luna passed Rewrite corporate jargon in plain words.
Against DeepSeek V4 Pro: GPT-6 Luna answered 1.6× sooner (2.4 s to 3.9 s), cost 10.8× less, and passed 5 of 5 to its 5.
Against Grok 4.7: GPT-6 Luna answered 2.5× sooner (2.4 s to 6.0 s), cost 57.8× less, and passed 5 of 5 to its 3. Only GPT-6 Luna passed Rewrite corporate jargon in plain words; Argue both sides of free buses.
Against Kimi K3: GPT-6 Luna answered 1.2× sooner (2.4 s to 3.0 s), cost 38.5× less, and passed 5 of 5 to its 4. Only GPT-6 Luna passed A product announcement with five rules.
Against GLM 5.3: GPT-6 Luna answered 1.4× later (2.4 s to 1.8 s), cost 5.8× less, and passed 5 of 5 to its 4. Only GPT-6 Luna passed Argue both sides of free buses.
Against GLM 5.3 Flash: GPT-6 Luna answered 3.5× sooner (2.4 s to 8.5 s), cost 3.2× less, and passed 5 of 5 to its 2. Only GPT-6 Luna passed Rewrite corporate jargon in plain words; A product announcement with five rules; Argue both sides of free buses.
Against Mistral Large 4: GPT-6 Luna answered 4.1× sooner (2.4 s to 9.8 s), cost 24.1× less, and passed 5 of 5 to its 4. Only GPT-6 Luna passed A product announcement with five rules.
How these runs were done
Rubric (graded). The grader model scores the reply from 1 to 5 on each published criterion. It passes with an average of 4 or more and no criterion under 3, and only if it also meets the prompt's automatic rules (length, words it must or mustn't use).
The grader is Claude Opus 5.5 at low reasoning effort; its own replies are graded by GPT-6 Astra, so no model grades itself. Its prompt and every rubric are on the methods page.
GPT-6 Luna, and writing, elsewhere
- GPT-6 Luna: price, limits and messages on every plan
- The best AI for writing: our picks among every model
- GPT-6 for writing
- GPT-6 Luna for coding: our test runs
- GPT-6 Luna for math: our test runs
- GPT-6 Luna for data analysis: our test runs
- Claude Haiku 5.5 vs GPT-6 Luna
- GPT-6 Luna vs DeepSeek V4.1 Flash
- GPT-6 Sol vs GPT-6 Luna
- Claude Haiku 4.5 vs GPT-6 Luna
- GPT-6 Astra vs GPT-6 Luna
- GPT-6 Luna vs Gemini 3.8 Flash
- GPT-6 Luna vs DeepSeek V4 Pro
- GPT-6 Luna vs Grok 4.7
- GPT-6 Luna vs GLM 5.3
- GPT-6 Luna vs GLM 5.3 Flash
- Rewrite for clarity: the prompt, and its price on each model
- AI prompts for writing, tested on four models
- Essay prompts for AI that help you write your own
- Our test runs: 50 prompts on every model
Questions
Is GPT-6 Luna good for writing?
In our test runs it passed 5 of 5 writing prompts, tied 1st of the 20 models in llmwise. Every reply is on this page, so you can judge them yourself.
How many of my messages does a writing reply from GPT-6 Luna use?
1 message each on Pro, where it has 60 a day on Pro. The price of a message is fixed and shown before you send it, however long the reply.
How were these runs done?
The same way for every model: each prompt sent through llmwise's own pipeline, each reply checked the same way. The methods page has every prompt and how each is scored.
Claude, GPT, Gemini, DeepSeek, Grok, Kimi, GLM, and Mistral, in one chat.
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