The X King has been renamed the Cross King as apparently that's how Conti intended it to be pronounced in the first place, but naturally everyone said "ex king". The tread pattern remains the same but I believe there have been some tweaks to the ProTection carcass to improve rolling resistance. Not sure about any subtle changes to other carcasses and the rubber compounds.
29 x 2.4" is no longer available, the closest now is 2.3". These are your choices in 29":
ProTection (folding, reinforced sidewalls, Black Chili compound): 2.2 and 2.3"
RaceSport (folding, lightweight sidewalls, Black Chili compound): 2.2 and 2.3"
ShieldWall System (folding, reinforced sidewalls, PureGrip compound: 2.0, 2.2 and 2.3"
Wire (wire bead, budget carcass and compound): 2.0, 2.2 and 2.3"
Only ProTection and ShieldWall are suitable for tubeless - the RaceSport carcass is too porous, and the Wire bead won't give a good seal to the rim. Black Chili is the best compound and gives good grip and is hard wearing; PureGrip is a bit cheaper and not quite as good, while the unspecified compound on the Wire sits at the bottom of the range.
Jenson do the ProTection in 29 x 2.3";
https://www.jensonusa.com/Continental-Cross-King-29-Tire
I've got a 27.5 x 2.2" Cross King RaceSport on Summer Bike at the front, and I haven't really noticed any difference between that and the same size X King RaceSport from the year before. It rolls really fast on the front and gives me all the grip I need in the Summer, and I've got it paired with a 27.5 x 2.2" Race King ProTection on the back.
I need a bit more grip on Winter Bike for the muddy conditions round these parts and here the Cross King doesn't quite hack it for me, so I've got a 2.25" Schwalbe Rocket Ron Addix Speed Snakeskin that works nicely. The Rocket Ron has a very similar tread pattern to the Cross King, but with slightly deeper knobs. The Snakeskin carcass isn't quite as tough as the ProTection but still OK, and though the Addix Speed compound is the hardest in the range it's still significantly softer than Conti's Black Chili, so grips a bit better, squirms a little more, and wears out a little faster.
