What is Hemmingway AI?

Hemmingway is an AI writing app with its own models, made by Hemmingway AI (Pty) Ltd, a company registered in South Africa. Its newest model, Hemmingway-1.5, is a 27-billion-parameter language model with open weights under the CC BY-NC 4.0 licence, trained for writing that sounds like a person wrote it: emails, messages, replies, posts, reviews and stories. 90% of its writing passes GPTZero & Pangram and the top AI detectors on the first try. You can use it in the Hemmingway apps for Mac, Windows and Android, in the browser at hemmingway.io, through an OpenAI-compatible API, or by downloading the weights and running it yourself.

Hemmingway-1.5 came out on 25 October 2026 and is the default in the app and the API. It is built on Hemmingway-1, the first model, which is still in the API and the app's model menu.

The name is spelt with two m's. Hemmingway is not connected to the writer Ernest Hemingway, and it is not the Hemingway Editor, a separate readability tool from a different company.

The short version

The models

Hemmingway-1.5

Hemmingway-1.5 is the model Hemmingway writes with. It is built for anything a person will read: emails, texts, replies, product descriptions, blog posts, reviews, forum comments, stories and speeches. Paste in text from another AI and it rewrites it in a person's voice.

Its headline result is the detector test. It wrote 1,848 texts in 13 kinds of writing, at every thinking level, each a first try with no picking and no retries. 90% passed GPTZero & Pangram and four of the top open AI detectors. Real human writing passes the same detectors 86% of the time, and Hemmingway-1 passed 7%. How the test was run, and every result on the model card.

It thinks before it answers, at its highest level unless you ask for less, and passes the detectors at every level. It reads pictures, supports function calling in OpenAI's format, and writes replies of up to 32,768 tokens, thinking included. Run it at temperature 1.0.

Hemmingway-1

Hemmingway-1 was the first model, released in September 2026. It was built for talking to people and for writing, and it gives you the text you asked for rather than a menu of options with notes attached. Ask most models for a text to your landlord and you get three versions and a paragraph explaining them. Hemmingway-1 gives you the text. Hemmingway-1.5 is built on it.

How Hemmingway-1 scores

Hemmingway tested Hemmingway-1 against the largest models available. Three of the tests below are Hemmingway's own benchmarks; EQ-Bench 4 is public, and Hemmingway ran it with the official harness. These are Hemmingway-1's scores, not Hemmingway-1.5's.

Our own tests are blind: answers are shuffled, every matchup is run in both orders, and the judge is a model that is not one of those being judged. All the scores are on Hemmingway-1's model card.

What they are good at

• Emails, texts and replies, especially the hard ones: saying no, asking for money back, telling someone something they will not like.
• Writing that reads like a person put it down, not a machine, down to passing AI detectors.
• Turning rough notes into a paragraph or a message in your voice.
• Letters, speeches, cards, poems and short stories.

What they are not good at

• Long fiction. Larger story models write better novels and long chapters. Fable 5 Max and GLM-5.3 scored higher on StoryBench.
• Languages other than English. They are English-first.
• Being a general assistant. They are built for writing, not for code.

The apps

The Hemmingway app runs on Mac, Windows and Android, and in the browser at /app/. In it you can:

• ask it to write anything, from a two-line text to a short story;
• tell it who people are, in People, so it writes to your boss, a client or your sister the way you would;
• keep a Memory of things it should know, which you can read, change or delete line by line;
• have it look things up, read pictures and files you attach, and save what it writes as a PDF or a Markdown file.

In the apps for Mac, Windows and Android there is an Inbox. Connect your mail and it puts your mail and chats in one list and drafts each reply for you to read and send. It works with Gmail and Outlook, and the same Inbox holds WhatsApp, Slack and Teams, and iMessage on the Mac. Autopilot, in the Mac and Android apps on paid plans, can answer the easy messages by rules you set. It is off until you switch it on, and everything it does is listed with the reason.

The app is free to try, with no card needed. For plans, see /pricing/.

The apps are not yet signed by Apple or Microsoft or listed in the Play Store, so your computer or phone asks once before opening them.

The API

Both models are available through an OpenAI-compatible API. Requests go to https://hemmingway.io/v1 with a key from the API platform and the model hemmingway-1.5, the default, or hemmingway-1. The old id hemmingway-27b still works and means Hemmingway-1. Code that already uses OpenAI's SDKs needs the base URL, the key and the model name changed.

It supports streaming, function calling, up to four pictures a request, and control over thinking with reasoning_effort or enable_thinking. A key can draw on prepaid credit or on the allowance of your app plan. Web search and page reading are part of the app, not the API. The full reference is in the docs.

Running it yourself

Because the weights are open, you can run either model on your own hardware. With vLLM:

vllm serve HemmingwayAI/Hemmingway-1.5 --max-model-len 262144

For Hemmingway-1, use HemmingwayAI/Hemmingway-1. Both load in Transformers as normal chat models. The guides to running Hemmingway-1.5 and running Hemmingway-1 have the full examples, and there is more on open models for writing.

Try HemmingwayDownload the app

The name

Hemmingway has two m's. The models are Hemmingway-1.5 and Hemmingway-1, the app is Hemmingway, the company is Hemmingway AI (Pty) Ltd, and the site is hemmingway.io.

• Not Ernest Hemingway. The American novelist is spelt with one m. Hemmingway has no connection to him or his estate.
• Not the Hemingway Editor. Hemingway Editor, also with one m, is a readability tool at hemingwayapp.com that highlights hard-to-read sentences in what you wrote. It is a different product from a different company. Which is which.

If you search for "Hemmingway AI" and land on either of those, that is why.

Privacy

Hemmingway never trains its models on your chats, memory or People. On the web and on Android you can keep chats only on your device. The privacy page lists everything that is kept.

Common questions

What is Hemmingway AI?

Hemmingway is an AI writing app whose model, Hemmingway-1.5, writes emails, messages and stories that sound like a person wrote them: 90% of its writing passes GPTZero & Pangram and the top AI detectors. Hemmingway-1.5 is a 27B open-weights model under CC BY-NC 4.0, built on Hemmingway-1. You can use it in apps for Mac, Windows, Android and the web, or through an OpenAI-compatible API.

Who makes Hemmingway AI?

Hemmingway AI (Pty) Ltd, a company registered in South Africa, with a team in South Africa and Switzerland. It makes Hemmingway-1.5, Hemmingway-1, the Hemmingway apps and Hemmingway Unlocked. More about us.

Is Hemmingway the same as the Hemingway Editor?

No. Hemmingway, with two m's, writes for you. Hemingway Editor, with one m, is a separate tool from a different company that highlights hard-to-read sentences in text you have already written.

Is Hemmingway open source?

Its models have open weights rather than open source. The weights are on Hugging Face at huggingface.co/HemmingwayAI/Hemmingway-1.5 and huggingface.co/HemmingwayAI/Hemmingway-1 under CC BY-NC 4.0, free for non-commercial use, and the code is on GitHub at github.com/lukeckprobierts/Hemmingway-1. Commercial use is by agreement with us: write to luka@hemmingway.io.

What model is Hemmingway built on?

Hemmingway-1.5 is built on Hemmingway-1, which is built on Qwen3.8-27B and trained further for writing. Both have the same 27B size and a 262,144-token context. How Hemmingway-1 differs from the base model.

Is Hemmingway free?

The app is free to try, with no card needed, and the model weights are free to download and run for non-commercial use. For paid plans and API costs, see /pricing/ and the API platform.