A platform explains what a character definition controls

What happened

Character.AI, the company behind one of the largest companion-style chat platforms, publishes a creator-facing guide describing how to build a character. As retrieved on 16 September 2026, the guide's character attributes page lists the fields a creator can fill in: a name and greeting are required, and a short description, long description and a free-text "definition" field are optional additions a creator can use to describe the character in more depth. The guide is a living document, not a dated announcement, so this record describes the platform's stated design as it currently reads rather than a single historical event.

What the documents show

The attributes page states directly that "most of these items are optional, and supplying more information won't necessarily make a particular character closer to your vision," and separately notes that some fields, including avatar image and category tags, "do not currently influence the Character behavior, though some could in future updates." The guide's overview adds that a character's responses are shaped by four things together: the attributes a creator sets, ongoing training from in-conversation signals such as star ratings, the persona and preferences a user has set for themselves, and the immediate conversation context. No single field is presented as a fixed script the model must follow.

The mechanism

The mechanism the guide describes is a persona prompt combined with a live feedback loop, not a hand-authored script or a dedicated fine-tuned model for each character. Text a creator writes into the definition and example-dialogue fields is inserted into the underlying model's context, the same conditioning approach the Persona-Chat research popularised, and the model then generates a reply consistent with that context as best it can. Because a large general-purpose model sits underneath, the guide itself acknowledges the model can drift toward whatever direction a user's conversation pulls it, which is why the page asks, rhetorically, how a character can "know" to consistently act as something as narrow as a refrigerator: a written definition constrains a probability distribution over text, it does not hard-code a rule.

What it leaves open

The guide does not state how much weight each of the four listed factors carries relative to the others, nor does it describe the underlying model or the training pipeline used to build in-conversation adaptation from star ratings. It is the company's own creator documentation, describing intended design rather than an independent test of how reliably characters stay in character. Whether a given deployed character behaves as its definition suggests is a claim this record does not verify.

• Does the definition text stay visible and editable to the creator, or is it hidden once published?
• What happens to a character's behaviour when a user's messages contradict the stated definition?
• Does the platform document how user ratings retrain or adjust an individual character over time?

The plainest lesson in the company's own documentation is a caution: a character definition is an instruction to a general model, and the guide asks creators to treat it as a set of tools to experiment with, not a strict guide to guaranteed behaviour.