13 speed makes a lot of sense when you consider it's built around the 1x concept. SRAM have increased the size of the largest cog to create a 10 - 46 tooth cassette and then used the fact that they can squeeze 13 cogs in there to minimise the jumps between the gears. Also it appears to also fit onto the normal 11 or 12 speed XDR Driver hub which is great for any folk considering an upgrade.
The big issue with this though, is yet again it's aimed at the racing/smooth gravel road market. Despite being 13 speed it only has a 460% range and with the stock crankset only offering 38 teeth as the smallest size, the gearing is far too high for folk like me who enjoy the more adventurous side of gravel biking.
For those of you who favour multiple chainrings on the front, here's a comparison with Shimano's 2x GRX gravel groupset, which just like SRAM's 13 speed, is geared far to highly for series gravel adventurous riding, though overall range at 502% is much better.
Another big drawback of 13 speed is that it's only available on their top tier Red groupset and the price is accordingly high, over €675 just for a cassette! utter flipping madness.