No one uses any codec 'exclusively' because you need the client devices to be able to decode what you serve them. I think the current strategy is that they have

No one uses any codec 'exclusively' because you need the client devices to be able to decode what you serve them. I think the current strategy is that they have AV1 for large/popular media, then h265 and ultimately h264 as fallbacks. Client-side hardware support is what holds AV1 back currently.