Question about controller.input_pos

I’m using Position Control Mode.

My question is, is the value of controller.input_pos something that remains static after cycling power?

Or is it an arbitrary or relative value upon power up?

It is reset every time you enter closed loop contol.
By default it is relative to the position when the ODrive booted up, but you can use absolute position mode and homing to make it with respect to an absolute reference instead