Shimano have just announced 12-speed XT and SLX group sets - and we've ridden them.
Chains and cassettes with Shimano Deore XT and SLX
Visually these are very similar to the XTR units. Both come in either a 10-51 or 10-45 option. On XT there are 2 alloy sprockets and the rest are steel. On SLX there is 1 alloy sprocket. Unlike XTR there are no Titanium sprockets, for obvious reasons to keep the costs where they should be. The cassettes still have the beam spider construction, which is lighter and stiffer than complete sprockets running to the freehub body.
The cassettes all require the Microspline freehub, and there are XT and SLX level hubs that are also released.
A chain is a chain is a chain - right? Well yes and no. You can mix and match the SLX, XT and XTR parts all you like. But the XTR chains are lighter, stronger and last longer. The higher end chains have different surface treatments which increase durability and reliability.
The SilTec coating actually reduces friction and increases the strength of the chain, and the hollow pin construction of the XTR chains is actually stronger, as the peening (or flaring) of the ends of the chain pins on a hollow pin actually flares out more for better security of the plates.
So if you only upgrade one item to XTR - your chain is a good place to do it.
All the chains come with quick links, and they are also a bit longer out of the box than before due to the chain requirements of a 51t sprocket.
This is the silent hero of Shimano 12-speed group sets, and yes that's a bit of a pun. Hyperglide was the innovation that Shimano had decades ago to make shifting smoother. It's the ramping and shaping of the cassette teeth (and chain rings, but we're all on 1x now, right?) and shape of the chain plates to make the downshift to lower gears (larger sprockets) much smoother. So instead of the top derailleur pulley just moving below the gear and hoping it engages in the next pedal stroke, the shape of the teeth and chain actively make it happen.
Hyperglide Plus extends that to the upshift to (going to a harder gear) and the chain actually stays engaged with the cassette the whole time. So even if you're shifting up or down under load, it keeps driving the cassette and therefore your rear wheel. Not only is it more secure, but it is faster, and even improves underload. So yeah, panic shifts into a pinch climb are good. Dumping gears to chase your mate down the trail - that's also fine. It's secure, and it's fast. And it does it all pretty quietly too.