Where? Apple and Microsoft are the only ones I've seen offering on-device AI. It's been proven that Google is lying about this on several occasions. Mostly with their photo editor.
Gemini Nano. It's in Pixel Recorder and Gboard but multimodal capabilities are coming soon. It's very limited to a couple phones and not many companies outside of Google have access, but it has been used in production since last year.
Apple does not have on device AI in production today. Microsoft's "Copilot+PCs" launched less than 2 weeks ago, but are significantly more powerful machines.