Fay

Fay is a Python framework for building AI-powered digital humans: virtual on-screen characters that can speak, listen, and carry on conversations. It acts as a bridge between visual avatar software (2.5D and 3D models, Unity, Unreal Engine, mobile apps, web pages) and the large language models that power the conversation. You set up a character appearance with one system and connect Fay to give it a voice, a personality, and real-time responses.

On the language model side, Fay connects to any OpenAI-compatible API, including DeepSeek and locally hosted models, and lets you swap the model out without changing the rest of the setup. Speech recognition and text-to-speech modules are also interchangeable, so you can use different providers depending on quality or cost. The framework streams responses as they are generated, which means the character can begin speaking before the full reply is ready.

Built-in modes include a virtual teacher, a virtual live streamer, and a news broadcast reader, where the character delivers prepared or generated content automatically on a schedule. There is also an interactive mode with voice and text input, wake-word detection to start conversations, and an agent mode where the character can call external tools on its own to answer questions or complete tasks. A knowledge base and a custom Q&A file let you shape what the character knows and how it responds.

The framework runs on Windows, macOS, and Ubuntu with Python 3.12. A management interface is accessible via a local web page for configuration and control. The project is fully open source, and the README states it is free to use for commercial purposes.