The phones not out yet, but you can grab the wallpapers for the pixel 4 here.
https://9to5google.com/2019/09/27/download-google-wallpapers-pixel-4/
https://9to5google.com/2019/09/27/download-google-wallpapers-pixel-4/
Follow along with the video below to see how to install our site as a web app on your home screen.
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The Pixel 2 had some live wallpapers that were amusing for a few minutes - I quite liked the way they were almost static images but if you looked closely you would realise they were not. But TBH I've never been a huge fan of live wallpapers per se, even less so of using one which everyone else with the phone will have. But for those that like them, sure.
I'm more interested in a proper release of the theming app. Right now you can change accent colours and fonts through the developer options (though the font choice is "default" or "horrible" - they don't call them that, of course), but you lose your choices after a restart. A proper, persistent choice, and a wider range of fonts would be nice (it would be too much to hope for Google to give up enough control to let you load your own...)