It's a bit larger, more in the range of the 777 than the 787.
Roughly, it used to be A330 vs 767 and A340 vs 777, the A330 and the 777 were the winners in these segments. The 787 was built to beat the A330, and it did, and the A350 was built to beat the 777, and it might.
Airbus reacted to the 787 with a re-engined A330, the A330neo, which was not a great success, but not a total flop. Boeing re-engined and enlarged the 777 to create the 777X, whose smaller variant positioned against the A350 is a slow seller, but whose larger variant, which has no direct competitor, has seen some sales - if Boeing manages to get it out of the door, the program is again hugely delayed and over budget.
