How do AI girlfriend apps work?

The three systems working together

1. The language model. Every reply is generated by a large language model, the same class of technology behind modern AI assistants. The app gives it a hidden character sheet: name, age, personality, speaking style, backstory. That is why Aria teases you and Emma reassures you when you type the exact same sentence to both.

2. The memory layer. Important details from your chats (your name, your job, your dog, your plans) are extracted and stored. Before each reply, the app retrieves the relevant memories and hands them to the model. Done well, she casually references your Tuesday interview on Friday. Done badly, she asks your name for the third time. Memory quality is the single biggest difference between apps.

3. The voice pipeline. For calls, your speech is transcribed, the model generates a reply, and text-to-speech renders it in the companion's voice, all fast enough to feel like a phone call. Luna treats calls as a first-class feature rather than an afterthought, which is why the app's full name is Luna AI: Girl Chat & Calls.

Why she feels different from ChatGPT

General assistants are trained to be neutral, helpful and forgettable. Companion apps tune the same underlying technology in the opposite direction: strong opinions, consistent moods, flirting, running jokes, and emotional continuity from one conversation to the next. She also has her own life details to draw from, so conversations go both ways instead of feeling like an interview.

The other difference is initiative. A companion in Luna can text you first or ring you, because a relationship where you always start every conversation stops feeling like one. More on that in how AI calls work.