Undetectable AI is a humanizer. You write something with ChatGPT or another AI, paste it in, and it rewrites the text so AI detectors read it as human. Hemmingway starts one step earlier. Its model, Hemmingway-1.5, writes the text itself, and what it writes is meant to read as a person's from the first draft: in our own published test, 90% of it passed GPTZero and four other top AI detectors on the first try.
So the question is where you start. If you already have AI text and want it reworked, that is what Undetectable AI is built around, and Hemmingway can do it too. If you are starting from what you want to say, Hemmingway saves the step. We have not tested Undetectable AI, so this page compares what each is, from its own site, not which scores higher. Hemmingway-1.5's own result, with the method, is on our page about undetectable AI.
The short version
| Hemmingway | Undetectable AI | |
|---|---|---|
| What it is | A writing model and the app around it | A humanizer, with a detector and writing tools |
| Starts from | What you want to say, or text to rewrite | AI text you paste in |
| Detector result | 90% passed GPTZero and four other detectors, our test, method published | Says its output scores as human on "every major detector"; names none on its home page |
| Detectors named | GPTZero, Fakespot, Vanguard, WasItAIGenerated, MELD | None on its home page |
| Free use | Free to try, no card | Free trial up to 250 words |
| Paid plans | On pricing, from $9 a month | From $9.99 a month for 10,000 words, or $5 a month billed yearly |
| Open weights | Yes, CC BY-NC 4.0 | None listed on its site |
| Tested by us | Yes | No |
Rewriting and writing are different jobs
A humanizer works on a draft that already exists. Undetectable AI's site says its humanizer takes text that feels stiff or robotic and makes it natural, and its FAQ says it varies sentence structure, vocabulary and tone in the parts a detector flags. That is useful when the draft is right and only the style is off.
What a rewrite cannot easily fix is a draft that says the wrong thing, or says it in a way that is generic underneath. If the first AI padded it, invented a detail or missed the point, the humanized version keeps the padding, the detail and the miss, in new words.
A writing model needs only the facts. Tell Hemmingway who it is for and what you want said, and it writes the text once, in the register the reader needs, with nothing around it to cut. AI humanizer vs AI writer goes into the difference.
The detector results
Ours are our own, and here is all of it. Hemmingway-1.5 wrote 1,848 texts in 13 kinds of writing, at all four thinking levels. Each went through GPTZero, Fakespot, Vanguard, WasItAIGenerated and MELD once, with no picking and no retries. 90% passed. GPTZero on its own passed 90% at every thinking level. Real human writing passed the same detectors 86% of the time, and Hemmingway-1, our first model, passed 7%. When Hemmingway-1.5 rewrites AI text instead of writing from scratch, 89% of its rewrites passed, by its Hugging Face card. The method is on the model card and in our AI detector test.
Undetectable AI's home page says its output scores as human on every major detector. It does not name the detectors there, and we have not tested it.
A worked example
Say a recruiter offered you a job at a salary well under what you earn, and you want to say no unless the budget changes.
With a humanizer, you first ask a chatbot for the reply, then paste its answer in to be rewritten. If the chatbot's reply was three paragraphs of thanks with the actual no in the middle, the rewrite is three paragraphs of thanks in different words.
With Hemmingway, you give it the facts in a line:
Reply to Marisa. Thanks, but the salary is well below the market for my level. Not interested unless the budget is higher. Short.
You get one short reply that a recruiter could get from you. An ask like this one is in the test. By the model's Hugging Face card, Hemmingway-1.5's reply to it read as human, and the replies from Fable 5.1, GPT-6 Astra and Gemini 3.8 Flash were flagged as AI. Across all 80 everyday asks in that comparison, 92% of Hemmingway-1.5's answers passed.
When Undetectable AI fits
- You already have text from another AI and only want it reworded.
- You want a detector and a humanizer in one place, and the image and audio detectors its site also lists.
- You write in a language other than English: Hemmingway is English-first.
When Hemmingway fits
- You have not written anything yet and do not want to write it twice.
- The text goes to a person under your name: an email, a reply, a post, a review, a product listing.
- You want a result with a published method, and open weights you can run yourself.
- You want the app to draft replies from your inbox. In the Mac, Windows and Android apps, it drafts replies for you to send. Nothing goes out until you do.
Privacy
We never train our models on your chats, memory or People. Our privacy page lists what we keep. For Undetectable AI, read its own policies.
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Common questions
Is Hemmingway better than Undetectable AI?
They do different jobs, and we have not tested Undetectable AI, so we cannot score them against each other. Hemmingway-1.5 writes text that passed GPTZero and four other detectors 90% of the time in our published test. Undetectable AI rewrites text another AI wrote.
Can Hemmingway humanize AI text like Undetectable AI does?
Yes. Paste the text in and ask for it in a person's voice. By its Hugging Face card, 89% of Hemmingway-1.5's rewrites of AI text passed the same detectors. The AI humanizer opens the app with your text filled in.
Which detectors does Hemmingway pass?
In our test: GPTZero, Fakespot, Vanguard, WasItAIGenerated and MELD, together, 90% of the time on the first try.
Is Hemmingway free?
It is free to try, with no card needed. Plans are on pricing. The model's weights are open and free for non-commercial use.
Is there an undetectable AI that does not need a humanizer?
That is what Hemmingway-1.5 is for. See undetectable AI for the test and the numbers.