Hydraulic Disc Brake Dual Control Lever
Shimano GRX supports disc brakes only and this makes sense considering the improved tyre clearance and better performance under rough conditions. Its ergonomics (shape) were redesigned to improve comfort and control on bumpy terrain (it has anti-slip ridges on the hood).
Each lever has 2 E-tube ports. It does not have a dedicated sprint shifter port, so you cannot use the SW-R610 with these levers.
The weight of 373g is for a pair of levers, not a single lever.
The clamp band inner diameter is 23.8-24.2mm.
Cable actuated disc brakes
Even though I strongly recommend you use the GRX hydraulic disc brakes, there are no doubt people wanting to run cable-actuated disc brakes due to financial reasons. In that case you will not be able to use the GRX levers. These levers support hydraulic disc brakes only. You can use any other Shimano Di2 Dual Control Lever though, like the ST-6870, ST-9070, ST-R8050 or ST-R9150
The GRX ergonomics are excellent for gravel riding, but if you're looking for other hydraulic disc levers, have a look at the Ultegra ST-R8070 and Dura-Ace ST-R9170.