With most assistants, the user can dictate a prompt and the assistant can “read aloud” its response. Some models e.g. ChatGPT have an advanced voice mode where users can have a fluid back-and-forth conversation with the AI assistant, in English and other languages.

ChatGPT’s Dictate and Voice Mode is available from the icons on the right of the prompt box.

ChatGPT’s Voice Mode in action.
Technical note Under the covers, the model is responding to an audio speech prompt and directly providing a speech response. It is not using text as an intermediate part of this process (apart from transcribing into text after the fact if required)