What is Character.AI, and how do its chatbot characters work?

A new chatbot site opened its doors yesterday. Character.AI lets you hold a text conversation with a character, a famous historical figure, a fictional hero, a helpful tutor or something entirely invented, and lets anyone build new characters for others to talk to. Until now the service had a waitlist; as of 16 September 2022 it is open to the public as a beta.

The company describes itself as an AI startup chasing a familiar science-fiction dream: talking freely with a computer about anything. It sees uses in entertainment, education and answering general questions.

Who is behind it

Character.AI was founded in November 2021 by Noam Shazeer and Daniel De Freitas, both previously engineers at Google. De Freitas was the lead designer of Meena, an experimental Google chatbot that later became LaMDA. The company's home page lists a team of eleven, among them Romal Thoppilan, Myle Ott, Irwan Bello and Vinay Rao alongside the two founders.

That background matters. Building a chatbot that stays in character, keeps a conversation going and responds naturally is exactly the kind of problem this team worked on before.

How the characters work

The site's own FAQ gives a refreshingly plain explanation. The beta runs on neural language models: programs that read enormous amounts of text and learn to predict which words are likely to come next in any situation. The same kind of technology powers auto-complete on phones and machine translation.

Character.AI turns that prediction into a conversation. You write one character's lines, your own, and the computer writes the other character's lines, which gives the feeling of talking with that character. A name, a greeting and a description act as the starting context, so the model "plays" that role as it continues the dialog.

Several features shape the experience:

Choosing replies: you can swipe left or right to see other possible answers and pick the best one.
Shaping a character: when you build a character, your questions and answers in a few practice chats help guide how it behaves.
Rooms: you can create a room with several characters and a topic, such as a play-by-play superhero battle, and the characters try to follow it.
Visibility: each character can be public, unlisted (anyone with the link) or private.

What a character is made of

Creating a character takes three quick steps, with optional extras. Here is how the pieces fit together, using a made-up example:

Field	What it does	Example
Name	Who the character is	Professor Ada
Greeting	The first thing it says	"Hello! I teach chemistry. What would you like to understand today?"
Visibility	Who can chat with it	Public
Short description	A few words on how it sees itself	"Patient chemistry teacher"
Long description	A few sentences of personality and background	"Loves kitchen experiments, explains with everyday examples, never makes students feel silly."

The site's own suggestion for a greeting is a historical figure introducing themselves: a character named after Albert Einstein might open by mentioning his birth date and his theory of special relativity. The greeting sets the tone, and the language model takes its cue from it.

Try it: Before building anything, write a greeting and a two-sentence description for a character you would find useful, such as a patient language-practice partner. Then write the first three questions you would ask it. Notice how much the greeting already decides about the tone of the answers you expect.

Why it matters

Character.AI puts a conversational language model directly in front of the general public, with no programming and no waitlist. The model is wrapped in something familiar: a chat with a personality.

It also hands the creative work to users. Instead of one official assistant, the site hosts as many characters as people care to make, and anyone can share theirs. That makes it a large, open experiment in what people actually want to do with conversational AI, whether that turns out to be play, study, practice or company.

How can you create your own character, and what should you keep in mind?

To create one, sign up at beta.character.ai, choose "Create a Character" and fill in the name and greeting; the visibility setting decides whether others can find it. You can then add short and long descriptions, try a few example chats, and use the swipe feature to pick the replies that best fit the personality you have in mind. Those choices help steer the character.

The most important thing to keep in mind is printed right on the chat screen: "Remember: Everything Characters say is made up!" The FAQ is just as frank, warning that the system is not a source of reliable information. A character named after a scientist does not know what that scientist knew; it produces text that sounds like them. Treat facts, dates and advice from any character as something to check elsewhere.

Used with that in mind, the site can be good for imagination, brainstorming and language practice, the uses its makers suggest. A practical approach is to give your character a clear purpose, such as quizzing you on vocabulary or playing a role in a story, rather than asking it to be an expert. It is also wise not to share personal details in a chat, as you would with any new online service.