> A unique feature of JPEG XL is that it is possible to recompress existing JPEG images (of which there are a lot out there!) to a JPEG XL file that is on average about 20% smaller, without introducing any loss. In fact, the bit-exact same JPEG file can be reconstructed from the JPEG XL file.

I wasn't aware of this and this is actually crazy, and freaking brilliant from a migration point of view. I wonder how that was achieved. I didn't care so much about JPEG XL, now thanks to Google derping I want it everywhere.