Google launched AI Overviews in the United States in May 2024 and extended them to other countries and languages over the following year. They appear on questions where Google judges that a summary helps, and they push the classic results further down the page.
Being cited in an overview depends on the same signals as ranking: a page that answers the question clearly, is indexed, and is consistent with other sources. Google states that no special markup or file is needed, and that its usual guidance applies. For a business, the practical change is that some visits become a mention without a click.