GPT-⁠6 Luna

Q: How do I use GPT-6 for free?

Pick GPT-6 Luna in the chat at the top of this page, type your message and sign in with Google or Apple when asked. GPT-6 Luna is the GPT-6 model on the free plan of Overchat AI. GPT-6.1 Terra, GPT-6.1 Sol and GPT-6 Astra are on the paid plans.

Q: What is GPT-6 Luna?

GPT-6 Luna is OpenAI's fast, low-cost model of the GPT-6 family, released on September 22, 2026 together with GPT-6 Sol. It reads text, images and files, holds about 1 million tokens and is built for everyday chat, writing and coding.

Q: Is GPT-6 Luna as good as GPT-6 Astra?

No. GPT-6 Astra is OpenAI's top model: it scores 73.2% on DeepSWE v1.1 against 66.6% for GPT-6 Luna and 41.4% on AutomationBench against 20.7%. GPT-6 Luna answers faster and is free on Overchat AI, so use it for everyday tasks and switch to GPT-6 Astra in the same chat for hard ones.

Q: Is GPT-6 Luna better than GPT-5.6 Luna?

Yes. GPT-6 Luna scores 66.6% on DeepSWE v1.1 against 62.2% for GPT-5.6 Luna, 5.4 points more on AutomationBench at high effort, and makes 7.6% factual errors against 12.0%.

Q: Can GPT-6 Luna read images and files?

Yes. GPT-6 Luna takes text, images and files, such as PDFs and screenshots. On Overchat AI, attach a file to your message and ask about it.

Q: What is the context window of GPT-6 Luna?

GPT-6 Luna holds about 1 million tokens in one conversation, around 750,000 words, and writes up to 128,000 tokens in one answer.

OpenAI's fast GPT-⁠6 model for everyday writing, notes and code, free on Overchat AI, with a 1M-⁠token context

About GPT-⁠6 Luna

GPT-⁠6 Luna is the smallest and fastest model of OpenAI's GPT-⁠6 family, below GPT-⁠6.1 Terra, GPT-⁠6.1 Sol and GPT-⁠6 Astra. It reads text, images and files, holds about 1 million tokens in one conversation and writes up to 128,000 tokens in one answer

GPT-⁠6 Luna solves 66.6% of the real software tasks in DeepSWE v1.1, close to Claude Opus 5 at medium effort, and makes 37% fewer factual mistakes than GPT-⁠5.6 Luna. It scores 83.3% on AA-LCR, the best result among the models it is compared with at reading very long documents

GPT-⁠6 Luna is free on Overchat AI: a free account gets 100 credits every day with no card, and a GPT-⁠6 Luna message takes 3 of them. In the same chat you can switch to Claude, Gemini or DeepSeek

Developer

OpenAI

Released

Sep 22, 2026

Context window

1M tokens

Max output

128,000 tokens

Input

Text, images and files

Output

Text

Reasoning

Adjustable, from low to max

Intelligence Index

28, #25 of 54 models

Available in

OpenAI API, Codex, OpenRouter, Overchat AI

Modalities
Intelligence Index?: 28
Context window?: 1M tokens
Released: Sep 22, 2026

GPT-⁠6 Luna vs other models

GPT-⁠6 Luna ranks #25 on the Artificial Analysis Intelligence Index out of 54 models

Artificial Analysis Intelligence Index28#25 of 54 modelsBetter than 53% of 54 models

57GPT-6 Astra
55GPT-6.1 Sol
51GPT-6.1 Terra
36Claude Haiku 5.5
35Grok 4.7
33DeepSeek V4.1 Flash
31Gemini 3.8 Flash
29MiniMax M3.1 Flash
28GPT-6 Luna
23DeepSeek V4 Pro

#9of 183 modelsAA-LCRQuestions that need reasoning over very long documents83.3%
#15of 77 modelsMMMU ProCollege-level questions about charts, diagrams and photos79.7%
#16of 37 modelsFrontierCodeCode changes an agent writes, graded on whether they are ready to merge41.9%
#20of 187 modelsCritPtResearch-level physics problems19.4%

Source: Artificial Analysis

Compare GPT-⁠6 Luna

GPT-6 Luna vs GPT-6.1 Terra

GPT-⁠6 Luna scores higher than GPT-⁠6.1 Terra in 2 of 8 benchmarks. The widest lead is in FrontierCode: 41.9% against 36.0%. GPT-⁠6.1 Terra is ahead in Terminal-Bench 4.0: 55.6% against 12.6%. GPT-⁠6 Luna writes 143 tokens per second, GPT-⁠6.1 Terra writes 75

Benchmarks won: GPT-6 Luna: 2; GPT-6.1 Terra: 6
Average score: GPT-6 Luna: 42.9%; GPT-6.1 Terra: 51.4%
Output speed, tokens/s: GPT-6 Luna: 143; GPT-6.1 Terra: 75
Time to first token, s (log scale): GPT-6 Luna: 2.4; GPT-6.1 Terra: 4.3

GPT-6.1 Terra aheadGPT-6 Luna ahead

FrontierCode+5.9
AA-LCR+0.6
SciCode−0.5
AutomationBench−7.0
Humanity's Last Exam−7.7
AA-Omniscience−8.0
CritPt−8.6
Terminal-Bench 4.0−43.0

GPT-6 Luna vs Claude Haiku 5.5

GPT-⁠6 Luna scores higher than Claude Haiku 5.5 in 5 of 8 benchmarks. The widest lead is in AutomationBench: 53.2% against 35.4%. Claude Haiku 5.5 is ahead in Terminal-Bench 4.0: 32.8% against 12.6%. GPT-⁠6 Luna writes 143 tokens per second, Claude Haiku 5.5 writes 167

Benchmarks won: GPT-6 Luna: 5; Claude Haiku 5.5: 3
Average score: GPT-6 Luna: 42.9%; Claude Haiku 5.5: 43.2%
Output speed, tokens/s: GPT-6 Luna: 143; Claude Haiku 5.5: 167
Time to first token, s (log scale): GPT-6 Luna: 2.4; Claude Haiku 5.5: 2.1

Claude Haiku 5.5 aheadGPT-6 Luna ahead

AutomationBench+17.8
AA-Omniscience+4.9
AA-LCR+0.6
CritPt+0.5
FrontierCode+0.1
SciCode−0.4
Humanity's Last Exam−5.9
Terminal-Bench 4.0−20.2

GPT-6 Luna vs Gemini 3.8 Flash

GPT-⁠6 Luna scores higher than Gemini 3.8 Flash in 3 of 8 benchmarks. The widest lead is in FrontierCode: 41.9% against 36.4%. Gemini 3.8 Flash is ahead in AA-Omniscience: 50.5% against 39.6%. GPT-⁠6 Luna writes 143 tokens per second, Gemini 3.8 Flash writes 203

Benchmarks won: GPT-6 Luna: 3; Gemini 3.8 Flash: 5
Average score: GPT-6 Luna: 42.9%; Gemini 3.8 Flash: 46.3%
Output speed, tokens/s: GPT-6 Luna: 143; Gemini 3.8 Flash: 203
Time to first token, s (log scale): GPT-6 Luna: 2.4; Gemini 3.8 Flash: 7.5

Gemini 3.8 Flash aheadGPT-6 Luna ahead

FrontierCode+5.5
AA-LCR+2.0
CritPt+1.1
SciCode−2.0
AutomationBench−6.7
Terminal-Bench 4.0−7.1
Humanity's Last Exam−9.3
AA-Omniscience−10.9

GPT-6 Luna vs DeepSeek V4.1 Flash

GPT-⁠6 Luna scores higher than DeepSeek V4.1 Flash in 1 of 8 benchmarks. The widest lead is in AA-LCR: 83.3% against 82.7%. DeepSeek V4.1 Flash is ahead in Terminal-Bench 4.0: 33.8% against 12.6%. GPT-⁠6 Luna writes 143 tokens per second, DeepSeek V4.1 Flash writes 422

Benchmarks won: GPT-6 Luna: 1; DeepSeek V4.1 Flash: 7
Average score: GPT-6 Luna: 42.9%; DeepSeek V4.1 Flash: 48.7%
Output speed, tokens/s: GPT-6 Luna: 143; DeepSeek V4.1 Flash: 422
Time to first token, s (log scale): GPT-6 Luna: 2.4; DeepSeek V4.1 Flash: 2.2

DeepSeek V4.1 Flash aheadGPT-6 Luna ahead

AA-LCR+0.6
AA-Omniscience0.0
SciCode−1.3
FrontierCode−1.8
CritPt−4.6
Humanity's Last Exam−4.8
AutomationBench−13.4
Terminal-Bench 4.0−21.2

Best model by use case

Average benchmark scores of GPT-⁠6 Luna and 4 other models by use case

Coding
?Average of 3 tests
1. 1GPT-6.1 Terra48.9%
2. 2DeepSeek V4.1 Flash44.5%
3. 3Claude Haiku 5.543.2%
4. 4Gemini 3.8 Flash37.6%
5. 5GPT-6 Luna36.4%
Reasoning
?Average of 2 tests
1. 1GPT-6.1 Terra37.1%
2. 2DeepSeek V4.1 Flash33.6%
3. 3Gemini 3.8 Flash33.0%
4. 4Claude Haiku 5.531.6%
5. 5GPT-6 Luna28.9%
Knowledge work
?Average of 2 tests
1. 1Gemini 3.8 Flash65.9%
2. 2GPT-6.1 Terra65.2%
3. 3GPT-6 Luna61.5%
4. 4DeepSeek V4.1 Flash61.2%
5. 5Claude Haiku 5.558.7%
Agents
?AutomationBench
1. 1DeepSeek V4.1 Flash66.6%
2. 2GPT-6.1 Terra60.2%
3. 3Gemini 3.8 Flash59.9%
4. 4GPT-6 Luna53.2%
5. 5Claude Haiku 5.535.4%

GPT-⁠6 Luna benchmarks

Compare GPT-⁠6 Luna with 4 other models in 8 benchmarks measuring coding, reasoning, knowledge work and agents

Order

Coding

Terminal-Bench 4.0?12.6%−43.0
SciCode?54.6%−2.0
FrontierCode?41.9%−1.8

Reasoning

Humanity's Last Exam?38.5%−9.3
CritPt?19.4%−8.6

Knowledge work

AA-LCR?83.3%+0.6
AA-Omniscience?39.6%−10.9

Agents

AutomationBench?53.2%−13.4

Sources: OpenAI, Introducing GPT-6 Sol and Luna (Sep 22, 2026), Artificial Analysis, GPT-6 Luna

GPT-⁠6 Luna speed

Output speed is how fast the model writes (tokens per second, higher is better). Time to first token is how long you wait before the answer starts (lower is better)

Output speed and time to first token of 35 models

?Percentile

Time to first token, s (log scale)

Output speed, tokens/s (log scale)

Output speed and time to first token of 35 models
Models	Output speed, tokens/s (log scale)	Time to first token, s (log scale)
GPT-6 Luna	143	2.4
GPT-6.1 Terra	75	4.3
GPT-6.1 Sol	58	2.9
GPT-6 Astra	48	3.2
Claude Opus 5.5	88	1.9
Claude Opus 5	54	2.6
Claude Opus 4.8	59	1.3
Claude Fable 5.2	84	2.3
Claude Sonnet 5.5	102	1
Claude 5 Sonnet	215	10.5
Claude Sonnet 4.6	220	10.8
Claude Haiku 5.5	167	2.1
Gemini 4 Carbon	169	29.5
Gemini 4 Argon	91	6
Gemini 3.8 Flash	203	7.5
Gemini 3 Pro	270	11.2
Grok 4.7	81	8.9
Grok 4.6	290	32
Qwen 3.8 Max	81	30.6
DeepSeek V4 Pro	144	1.1
DeepSeek V4.1 Flash	422	2.2
Mistral Large 4	226	8.6
Hy4	214	37.7
ERNIE 5.5 Flash	405	2.7
Muse Wonder	980	8.7
Muse Spark	1129	6.2
Kimi K3.1 Pro	340	7.4
Kimi K3	338	5.9
GLM 5.3	197	1.2
Flint	194	12.3
Llama 4	81	0.7
Claude 4.5 Haiku	162	0.9
MiniMax M3	169	4.5
MiniMax M3.1 Flash	656	7.2
Kimi K2.7 Code	455	3.6

Typing test

Every model writes the same answer. The test waits the model's time to first token, then prints the text at the model's output speed and shows the total time

Answer length

GPT-6 Luna143 tokens/s2.4 s to first token
GPT-6.1 Terra75 tokens/s4.3 s to first token
Claude Haiku 5.5167 tokens/s2.1 s to first token
Gemini 3.8 Flash203 tokens/s7.5 s to first token

Source: Overchat AI, 2026-11-11

See how GPT-⁠6 Luna answers

Examples of GPT-⁠6 Luna answers to 3 prompts: Pull out action items, Write an email and Fix my JavaScript. Each answer is the unedited output of the model

Pull every action item out of these meeting notes as a table with the task, the owner and the due date: Kickoff with the design team, Monday. Anna will send the new logo options by Thursday. We agreed the landing page copy is Mark's job, first draft next Wednesday. Budget for ads is still open, Priya checks it with finance before the end of the month. Next sync in two weeks, Leo books the room.

GPT-6 Luna

Task	Owner	Due date
Kick off with the design team	Not specified	Monday
Send the new logo options	Anna	Thursday
Prepare the first draft of the landing page copy	Mark	Next Wednesday
Check the ad budget with finance	Priya	Before the end of the month
Book the room for the next sync	Leo	Before the next sync, in two weeks

Write a short, polite email to my landlord asking to fix the broken heater this week. It has been cold in the apartment for three days.

GPT-6 Luna

Subject: Heater Repair Request

Hi [Landlord’s Name],

Could you please arrange to have the broken heater fixed this week? The apartment has been cold for the past three days, and I’d appreciate your help resolving this as soon as possible.

Thank you,
[Your Name]

My JavaScript prints [object Promise] instead of the user data. Explain why in two sentences and fix it: const data = fetch('/api/user').then(r => r.json()); console.log(data.name);

GPT-6 Luna

fetch() is asynchronous, so data is a Promise and data.name is accessed before the user data has arrived. Use await inside an async function:

async function loadUser() {
  const response = await fetch('/api/user');
  const data = await response.json();
  console.log(data.name);
}

loadUser();

More prompts to try with GPT-⁠6 Luna

What GPT-⁠6 Luna is best for

Everyday writing
GPT-⁠6 Luna writes emails, messages, posts and replies in seconds, at about 140 tokens a second on Overchat AI
Notes and long documents
Paste meeting notes, a contract or a long report, and GPT-⁠6 Luna pulls out what matters. It scores 83.3% on AA-LCR, a test of reasoning over very long documents, ranking #9 of 183 models
Coding help
GPT-⁠6 Luna explains errors and fixes code, with 66.6% on DeepSWE v1.1, a test of real software tasks, close to Claude Opus 5 at medium effort
Photos and files
Attach a photo, a screenshot or a PDF and ask about it. GPT-⁠6 Luna scores 79.7% on MMMU Pro, a test of questions about charts, diagrams and photos

How to use GPT-⁠6 Luna on Overchat AI

Start in the chat at the top of this page or in the Overchat AI app on the web, iOS or Android

01
Pick GPT-⁠6 Luna
It is already picked in the chat on this page. In the Overchat AI app, open the model list next to the message field and pick GPT-⁠6 Luna
02
Attach your code or a file
Add code, a document, a spreadsheet or a screenshot, and write what you need: the result, the format and what must stay the same
03
Keep going in the same chat
Ask a follow-up, ask for tests or a shorter version, or switch to another model without losing the conversation

Why use GPT-⁠6 Luna on Overchat AI

One account for chat, images and video, on every device

Superchat picked over GPT-6 Luna: one request done by Claude Opus 5.5 (the plan) and Nano Banana 2.1 (the poster)

Superchat AI agent

Superchat Agent automatically routes your message to the model best suited for the task. It can generate images and videos, use the AI tools built into Overchat AI, and learn from your interactions to get better over time

Message field with a PDF, a spreadsheet and a dashboard screenshot attached, GPT-6 Luna picked and a voice message being recorded

Chat with images and files

Upload PDFs, spreadsheets, code and screenshots and ask GPT-⁠6 Luna about them. You can also dictate a message instead of typing it

An image made with Nano Banana 2.1 and a surfing video made with Seedance 2.5

Go beyond text

Generate images with Nano Banana and GPT Image and videos with Seedance and Kling in the same account, with the same credits as chat

On the web and iPhone

Start a chat on your laptop and finish it on your phone. The Overchat AI app has the same models, and your chats stay in one account on every device

GPT models on Overchat AI

Compare 4 GPT models on Overchat AI by output speed, time to first token and the price of one message

Models

Output speed, tokens/s

First token, s

Credits per message?

GPT-6 LunaThis page

143

2.4

GPT-6.1 Terra

4.3

GPT-6.1 Sol

2.9

GPT-6 Astra

3.2

Source: Overchat AI, 2026-11-11

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GPT-⁠6 Luna FAQ

If you have any questions,
reach out to us at hello@overchat.ai

Updated November 11, 2026

Yes, on Overchat AI. Sign up for free, no card needed: the free plan gives you 100 credits every day and a GPT-⁠6 Luna message takes 3 of them, so you get about 33 messages a day. On a paid plan a GPT-⁠6 Luna message takes 1 credit

Pick GPT-⁠6 Luna in the chat at the top of this page, type your message and sign in with Google or Apple when asked. GPT-⁠6 Luna is the GPT-⁠6 model on the free plan of Overchat AI. GPT-⁠6.1 Terra, GPT-⁠6.1 Sol and GPT-⁠6 Astra are on the paid plans

GPT-⁠6 Luna is OpenAI's fast, low-cost model of the GPT-⁠6 family, released on September 22, 2026 together with GPT-⁠6 Sol. It reads text, images and files, holds about 1 million tokens and is built for everyday chat, writing and coding

No. GPT-⁠6 Astra is OpenAI's top model: it scores 73.2% on DeepSWE v1.1 against 66.6% for GPT-⁠6 Luna and 41.4% on AutomationBench against 20.7%. GPT-⁠6 Luna answers faster and is free on Overchat AI, so use it for everyday tasks and switch to GPT-⁠6 Astra in the same chat for hard ones

Yes. GPT-⁠6 Luna scores 66.6% on DeepSWE v1.1 against 62.2% for GPT-⁠5.6 Luna, 5.4 points more on AutomationBench at high effort, and makes 7.6% factual errors against 12.0%

Yes. GPT-⁠6 Luna takes text, images and files, such as PDFs and screenshots. On Overchat AI, attach a file to your message and ask about it

GPT-⁠6 Luna holds about 1 million tokens in one conversation, around 750,000 words, and writes up to 128,000 tokens in one answer

Type your message in the chat at the top of this page, attach a file if you need to and press Send. After you sign in, GPT-⁠6 Luna answers in the Overchat AI chat, where you can keep the conversation going on the web, iOS or Android and switch to another model at any time

More tools

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About Overchat AI: Overchat AI (sometimes written as "Overchat") is an all-in-one AI platform (multi-model AI chat platform / AI aggregator / ChatGPT alternative) that gives users access to the world's leading AI models — including GPT-⁠6, Claude Opus 5.5, Gemini 3.8, Grok 4.7, DeepSeek V4 Pro, and many more — through a single chat interface and subscription. Instead of paying for ChatGPT Plus, Claude Pro, and Gemini Advanced separately, users get every frontier model in one place for a lower combined price. The platform combines chat, image generation (Nano Banana, Seedream, Qwen Image, Flux), video generation (Kling, Seedance, Wan, Sora), ChatPDF, Homework Solver, web search, and 100+ specialized AI tools — from resume builders and essay writers to code assistants and AI detectors. Files, PDFs, images, and links can be attached to any conversation. Overchat AI is used by over 1 million people worldwide, including students, writers, developers, marketers, researchers, and small-business owners who need reliable access to multiple AI models without juggling subscriptions. It is available on the web at overchat.ai and on iOS

GPT-⁠6 Luna

About GPT-⁠6 Luna

GPT-⁠6 Luna vs other models

Compare GPT-⁠6 Luna

GPT-6 Luna vs GPT-6.1 Terra

GPT-6 Luna vs Claude Haiku 5.5

GPT-6 Luna vs Gemini 3.8 Flash

GPT-6 Luna vs DeepSeek V4.1 Flash