The Dura-Ace CN-9000 11-speed chain is 9 grams lighter and 20% more durable than the CN-7901. The CN-9000 is 5.62mm wide - slightly more narrow than the 5.88mm 7901 chain. One nice feature is the 11-speed chain is symmetrical so there is no need to worry amount putting it on in the correct orientation - it can be put on in either direction.
One of the key features of the CN-9000 chain is the PTFE coating that contributes to a claimed 20% increase in durability. The PTFE coating also provides a smoother feel during shifts and less drivetrain noise even when cross-chaining. Chain pins for installation are included with the chain.
It's relatively cheap, and it shifts well for about two weeks. Then it wears and begins to shift poorly. I get about 3-4 weeks from this Shimano chain. Maybe the 11 speed design is necessarily thinner and weaker. However, the KMC 11 speed lasts longer - for a higher price.
We normally get 1500 miles out of a CN-9000 chain with proper cleaning and care - ed
Cons: Poor longevity, quality