Fast road riders who want aero on Giant's chart. TCR is the lighter, more conventional sibling.
Giant's aero race bike. Stiffer at the front, more wind-cheating than TCR, still in the same size-letter family so many riders can twin the two.
Gravel riders who want Giant's drop-bar all-road, not a TCR with knobbies.
Giant's gravel bike: stable, mounts, and a position between Defy and a race gravel whip. The X variants add more suspension/travel attitude.
Right now, Nino Schurter and Scott's pros. Someday soon, us mere mortals. This bike is for the folks who need cutting edge and aren't afraid of the early-adopter tax.
We don't know yet. The press and Scott have been tight-lipped. But we bet there's going to be some fun to be had now that 32" wheels seem to be making their way over from mountain bikes to gravel.