[Sakos]

Apparently Microsoft was granted this patent on rANS in early 2022 (https://patents.google.com/patent/US11234023B2/en) and Google deprecated JPEG XL support late 2022. JPEG XL uses rANS, so I think there's some likelihood that this motivated Google to change their focus. Google didn't mention anything about this in their reasoning, but would they have mentioned patent issues publicly if that were the real reason? Google isn't obligated to tell us everything and the reasons they gave always felt weak and weirdly dismissive.

[JyrkiAlakuijala]

JPEG XL doesn't use the kind of rANS that Microsoft has patented.

JPEG XL decides the codes at encoding time and does context modeling the same way as WebP lossless and Brotli, by deciding which entropy codes to use explicitly.

Microsoft's rANS patent is supposedly centralized around updating rANS codes at decoding time (based on past symbols). This is slightly more efficient for density, but much slower and may negate the speed benefits that rANS brings. For practical implementations JPEG XL/Brotli way is quite a bit better.